mm: zswap: remove unnecessary check in zswap_find_zpool()

zswap_find_zpool() checks if ZSWAP_NR_ZPOOLS > 1, which is always true. 
This is a remnant from a patch version that had ZSWAP_NR_ZPOOLS as a
config option and never made it upstream.  Remove the unnecessary check.

Link: https://lkml.kernel.org/r/20240311235210.2937484-1-yosryahmed@google.com


Signed-off-by: Yosry Ahmed <yosryahmed@google.com>
Reviewed-by: Chengming Zhou <chengming.zhou@linux.dev>
Reviewed-by: Nhat Pham <nphamcs@gmail.com>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Cc: Yosry Ahmed <yosryahmed@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>