mm/vmstat: fix a W=1 clang compiler warning

mm/vmstat: fix a W=1 clang compiler warning

Fix the following clang compiler warning that is reported if the kernel is
built with W=1:

./include/linux/vmstat.h:518:36: error: arithmetic between different enumeration types ('enum node_stat_item' and 'enum lru_list') [-Werror,-Wenum-enum-conversion]
  518 |         return node_stat_name(NR_LRU_BASE + lru) + 3; // skip "nr_"
      |                               ~~~~~~~~~~~ ^ ~~~

Link: https://lkml.kernel.org/r/20241212213126.1269116-1-bvanassche@acm.org
Fixes: 9d7ea9a297e6 ("mm/vmstat: add helpers to get vmstat item names for each enum type")
Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Cc: Konstantin Khlebnikov <koct9i@gmail.com>
Cc: Nathan Chancellor <nathan@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>