mm/shmem: fix functions documentation

Add missing parenthesis in @name parameter description.

Link: https://lkml.kernel.org/r/20250310112535.84754-1-enrico.bravi@polito.it


Signed-off-by: Enrico Bravi <enrico.bravi@polito.it>
Cc: Hugh Dickins <hughd@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>