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/[e-mail]
Signed-off-by: Yishai Hadas <[e-mail]>
Signed-off-by: Leon Romanovsky <[e-mail]>
Signed-off-by: Jason Gunthorpe <[e-mail]>

drivers/infiniband/core/umem.c

···
 	 */
 	pgsz_bitmap &= GENMASK(BITS_PER_LONG - 1, PAGE_SHIFT);
 
-	/* At minimum, drivers must support PAGE_SIZE or smaller */
-	if (WARN_ON(!(pgsz_bitmap & GENMASK(PAGE_SHIFT, 0))))
-		return 0;
-
 	umem->iova = va = virt;
 	/* The best result is the smallest page size that results in the minimum
 	 * number of required pages. Compute the largest page size that could