RDMA/ocrdma: Simplify code in 'ocrdma_search_mmap()'

'pd_bitmap' does not need to be const. Without it, it is possible to use
this variable when calling '__set_bit()'. This is less verbose and more
logical.

Link: https://lore.kernel.org/r/ec5cab9611ba062adea4cf8c98a63406ed510a71.1637868728.git.christophe.jaillet@wanadoo.fr


Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>