Fix the missing dbq_lock mutex initialization

Fixes: 2ad4e630 ("RDMA/bnxt_re: Implement doorbell pacing algorithm")
Signed-off-by: Kashyap Desai <kashyap.desai@broadcom.com>
Signed-off-by: Selvin Xavier <selvin.xavier@broadcom.com>
Link: https://lore.kernel.org/r/1692032419-21680-1-git-send-email-selvin.xavier@broadcom.comSigned-off-by: Leon Romanovsky <leon@kernel.org>