RDMA/qedr: Fix doorbell bar mapping for dpi > 1

Each user_context receives a separate dpi value and thus a different
address on the doorbell bar. The qedr_mmap function needs to validate
the address and map the doorbell bar accordingly.
The current implementation always checked against dpi=0 doorbell range
leading to a wrong mapping for doorbell bar. (It entered an else case
that mapped the address differently). qedr_mmap should only be used
for doorbells, so the else was actually wrong in the first place.
This only has an affect on arm architecture and not an issue on a
x86 based architecture.
This lead to doorbells not occurring on arm based systems and left
applications that use more than one dpi (or several applications
run simultaneously ) to hang.

Fixes: ac1b36e5 ("qedr: Add support for user context verbs")
Signed-off-by: Ariel Elior <Ariel.Elior@cavium.com>
Signed-off-by: Michal Kalderon <Michal.Kalderon@cavium.com>
Reviewed-by: Leon Romanovsky <leonro@mellanox.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>