Fix clang 15 warning in cxgbe

Clang 15 warns:

sys/dev/cxgbe/cudbg/cudbg_lib.c:2949:6: error: variable 'i' set but not used [-Werror,-Wunused-but-set-variable]
        int i = 0;
            ^

Apparently 'i' was meant as the current retry counter, but '1' was used
in the while loop comparison instead, making the loop potentially
infinite, if 'busy' never gets reset.

MFC after: 3 days
Reviewed by: np
Differential Revision: https://reviews.freebsd.org/D35834