nfs: remove empty if statement from nfs3_prepare_get_acl

Remove empty if statement from nfs3_prepare_get_acl and update comment to
follow the one from the referred fs/posix_acl.c:get_acl().

No functional change intended.

Link: https://lkml.kernel.org/r/20221130151231.3654-1-ubizjak@gmail.com


Signed-off-by: Uros Bizjak <ubizjak@gmail.com>
Cc: Trond Myklebust <trond.myklebust@hammerspace.com>
Cc: Anna Schumaker <anna@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>