lib/rhashtable: cleanup fallback check in bucket_table_alloc()

lib/rhashtable: cleanup fallback check in bucket_table_alloc()

Upon allocation failure, the current check with the nofail bits is
unnecessary, and further stands in the way of discouraging direct use of
__GFP_NOFAIL.  Remove this and replace with the proper way of determining
if doing a non-blocking allocation for the nested table case.

Link: https://lkml.kernel.org/r/20240806153927.184515-1-dave@stgolabs.net
Signed-off-by: Davidlohr Bueso <dave@stgolabs.net>
Suggested-by: Michal Hocko <mhocko@suse.com>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Cc: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>