net/mpich: Update to 5.0.1

Changes: https://www.mpich.org/2026/04/10/mpich-5-0-1-released/

Fix Process Manager logic
Fix PLIST_SUB logic
Fix Makefile format with portfmt

Reviewed by: thierry (mentor)
Approved by: thierry (mentor)
Differential Revision: https://reviews.freebsd.org/D56358