Doing min_t(int, foo, INT_MAX) doesn't work correctly, because if foo
is bigger than INT_MAX, then when treated as a signed integer, it will
become negative and hence such an expression is just an elaborate NOP.

Fix such cases in ehca to do min_t(unsigned, foo, INT_MAX) instead.
This fixes negative reported values for max_cqe, max_pd and max_ah:

Before:

        max_cqe:                        -64
        max_pd:                         -1
        max_ah:                         -1

After:
        max_cqe:                        2147483647
        max_pd:                         2147483647
        max_ah:                         2147483647

Based on a bug report and fix from Anton Blanchard <anton@samba.org>.
Signed-off-by: Roland Dreier <rolandd@cisco.com>