RDMA/core: Remove unused ib_find_exact_cached_pkey

The last use of ib_find_exact_cached_pkey() was removed in 2012
by commit 2c75d2cc ("IB/mlx4: Fix QP1 P_Key processing in the Primary
Physical Function (PPF)")

Remove it.

Signed-off-by: Dr. David Alan Gilbert <linux@treblig.org>
Link: https://patch.msgid.link/20241221014021.343979-3-linux@treblig.org


Reviewed-by: Kalesh AP <kalesh-anakkur.purayil@broadcom.com>
Signed-off-by: Leon Romanovsky <leon@kernel.org>