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/[email protected]
Fixes: 9d7ea9a ("mm/vmstat: add helpers to get vmstat item names for each enum type")
Signed-off-by: Bart Van Assche <[email protected]>
Cc: Konstantin Khlebnikov <[email protected]>
Cc: Nathan Chancellor <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

Author: bvanassche

include/linux/vmstat.h

@@ -515,7 +515,7 @@ static inline const char *node_stat_name(enum node_stat_item item)
 
 static inline const char *lru_list_name(enum lru_list lru)
 {
-	return node_stat_name(NR_LRU_BASE + lru) + 3; // skip "nr_"
+	return node_stat_name(NR_LRU_BASE + (enum node_stat_item)lru) + 3; // skip "nr_"
 }
 
 #if defined(CONFIG_VM_EVENT_COUNTERS) || defined(CONFIG_MEMCG)