mm/page_alloc: make alloc_node_mem_map() __init rather than __ref

alloc_node_mem_map() is never only called from free_area_init_node() that
is an __init function.

Make the actual alloc_node_mem_map() also __init and its stub version
static inline.

Link: https://lkml.kernel.org/r/20210716064124.31865-1-rppt@kernel.orgSigned-off-by: Mike Rapoport <rppt@linux.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/page_alloc.c

@@ -7515,7 +7515,7 @@ static void __init free_area_init_core(struct pglist_data *pgdat)
 }
 
 #ifdef CONFIG_FLATMEM
-static void __ref alloc_node_mem_map(struct pglist_data *pgdat)
+static void __init alloc_node_mem_map(struct pglist_data *pgdat)
 {
 	unsigned long __maybe_unused start = 0;
 	unsigned long __maybe_unused offset = 0;
@@ -7561,7 +7561,7 @@ static void __ref alloc_node_mem_map(struct pglist_data *pgdat)
 #endif
 }
 #else
-static void __ref alloc_node_mem_map(struct pglist_data *pgdat) { }
+static inline void alloc_node_mem_map(struct pglist_data *pgdat) { }
 #endif /* CONFIG_FLATMEM */
 
 #ifdef CONFIG_DEFERRED_STRUCT_PAGE_INIT