bnxt_en: Cap the returned MSIX vectors to the RDMA driver.

In an earlier commit to improve NQ reservations on 57500 chips, we
set the resv_irqs on the 57500 VFs to the fixed value assigned by
the PF regardless of how many are actually used.  The current
code assumes that resv_irqs minus the ones used by the network driver
must be the ones for the RDMA driver.  This is no longer true and
we may return more MSIX vectors than requested, causing inconsistency.
Fix it by capping the value.

Fixes: 01989c6b ("bnxt_en: Improve NQ reservations.")
Signed-off-by: Michael Chan <michael.chan@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>