RDMA/bnxt_re: Fix the offset for GenP7 adapters for user applications

User Doorbell page indexes start at an offset for GenP7 adapters.
Fix the offset that will be used for user doorbell page indexes.

Fixes: a62d6858 ("RDMA/bnxt_re: Update the BAR offsets")
Signed-off-by: Selvin Xavier <selvin.xavier@broadcom.com>
Link: https://lore.kernel.org/r/1702987900-5363-1-git-send-email-selvin.xavier@broadcom.com


Signed-off-by: Leon Romanovsky <leon@kernel.org>