libirdma: Drop clang-specific -ferror-limit.

This could use -fmax-errors on GCC, but tweaking the error limit is
unusual in the tree anyway. Just remove it.

Reviewed by: erj, imp, emaste
Differential Revision: https://reviews.freebsd.org/D36808

(cherry picked from commit c3a3d1fd6c7007e7088936e14fd9b4944b3a3054)