x11-wm/wlmaker: don't hardcode WRKSRC in debug log

$ wlmaker
[...]
(INFO) backend/wayland/backend.c:436 Starting Wayland backend
(INFO) wrkdirs/usr/ports/x11-wm/wlmaker/work/wlmaker-0.1-430-ged7a302/src/server.c:731 Output layout change: Pos 0, 0 (1280 x 720).
(INFO) wrkdirs/usr/ports/x11-wm/wlmaker/work/wlmaker-0.1-430-ged7a302/src/server.c:618 Server 0x3489a2c74000: Added output 0x3489a4acfb80
(INFO) wrkdirs/usr/ports/x11-wm/wlmaker/work/wlmaker-0.1-430-ged7a302/src/wlmaker.c:282 Starting Wayland compositor for server 0x3489a2c74000 at wayland-0 ...
(ERROR) wrkdirs/usr/ports/x11-wm/wlmaker/work/wlmaker-0.1-430-ged7a302/submodules/libbase/file.c:125 Failed realpath(/wrkdirs/usr/ports/x11-wm/wlmaker/work/wlmaker-0.1-430-ged7a302/icons/chrome-48x48.png, 0x820d1df10): errno(2): No such file or directory
(ERROR) wrkdirs/usr/ports/x11-wm/wlmaker/work/wlmaker-0.1-430-ged7a302/submodules/libbase/file.c:125 Failed realpath(/wrkdirs/usr/ports/x11-wm/wlmaker/work/wlmaker-0.1-430-ged7a302/icons/terminal-48x48.png, 0x820d1df10): errno(2): No such file or directory
(ERROR) wrkdirs/usr/ports/x11-wm/wlmaker/work/wlmaker-0.1-430-ged7a302/submodules/libbase/file.c:125 Failed realpath(/wrkdirs/usr/ports/x11-wm/wlmaker/work/wlmaker-0.1-430-ged7a302/icons/firefox-48x48.png, 0x820d1df10): errno(2): No such file or directory
(INFO) wrkdirs/usr/ports/x11-wm/wlmaker/work/wlmaker-0.1-430-ged7a302/src/dock.c:141 Created dock view 0x3489a2c9a000
(ERROR) wrkdirs/usr/ports/x11-wm/wlmaker/work/wlmaker-0.1-430-ged7a302/submodules/libbase/file.c:125 Failed realpath(/wrkdirs/usr/ports/x11-wm/wlmaker/work/wlmaker-0.1-430-ged7a302/icons/clip-48x48.png, 0x820d1df10): errno(2): No such file or directory
(INFO) wrkdirs/usr/ports/x11-wm/wlmaker/work/wlmaker-0.1-430-ged7a302/src/clip.c:262 Created clip view 0x3489a2c5c540
(INFO) wrkdirs/usr/ports/x11-wm/wlmaker/work/wlmaker-0.1-430-ged7a302/src/xdg_toplevel.c:183 Created window 0x3489a4ad0000 for wlmtk XDG toplevel surface 0x3489a474a800
(INFO) wrkdirs/usr/ports/x11-wm/wlmaker/work/wlmaker-0.1-430-ged7a302/src/xdg_shell.c:122 XDG shell: Toolkit window 0x3489a4ad0000 for surface 0x3489a2c5d300
(INFO) wrkdirs/usr/ports/x11-wm/wlmaker/work/wlmaker-0.1-430-ged7a302/src/xdg_decoration.c:268 XDG decoration request_mode for XDG surface 0x3489a474a400, content 0x3489a474a910: Current 0, pending 0, scheduled 2, requested 2. Set: 2
(INFO) wrkdirs/usr/ports/x11-wm/wlmaker/work/wlmaker-0.1-430-ged7a302/src/toolkit/window.c:309 Set server side decoration for window 0x3489a4ad0000: 1
(INFO) wrkdirs/usr/ports/x11-wm/wlmaker/work/wlmaker-0.1-430-ged7a302/src/server.c:731 Output layout change: Pos 0, 0 (0 x 0).
^C