eth: bnxt: make ulp_id unsigned to make GCC 12 happy

GCC array bounds checking complains that ulp_id is validated
only against upper bound. Make it unsigned.

Reviewed-by: Michael Chan <michael.chan@broadcom.com>
Link: https://lore.kernel.org/r/20220520061955.2312968-1-kuba@kernel.org


Signed-off-by: Jakub Kicinski <kuba@kernel.org>