IB/core: Drop WARN_ON() from ib_umem_find_best_pgsz()

The WARN_ON() issued as part of ib_umem_find_best_pgsz() blocked cases
when only page sizes larger than PAGE_SIZE were set, drop it to enable
those cases.

In addition, there is no need to have a specific check for zero
pgsz_bitmap, the function will do its job and return 0 at the end if
nothing match will be found.

Link: https://lore.kernel.org/r/20210304130501.1102577-2-leon@kernel.org


Signed-off-by: Yishai Hadas <yishaih@nvidia.com>
Signed-off-by: Leon Romanovsky <leonro@nvidia.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>