mm/bootmem: silence section mismatch warning - contig_page_data/bootmem_node_data

WARNING: vmlinux.o(.data+0x1f5c0): Section mismatch in reference from the variable contig_page_data to the variable .init.data:bootmem_node_data
The variable contig_page_data references
the variable __initdata bootmem_node_data
If the reference is valid then annotate the
variable with __init* (see linux/init.h) or name the variable:
*driver, *_template, *_timer, *_sht, *_ops, *_probe, *_probe_one, *_console,

Signed-off-by: Marcin Slusarz <[e-mail]>
Cc: Johannes Weiner <[e-mail]>
Cc: Sean MacLennan <[e-mail]>
Cc: Sam Ravnborg <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

mm/page_alloc.c

···
 }
 
 #ifndef CONFIG_NEED_MULTIPLE_NODES
-struct pglist_data contig_page_data = { .bdata = &bootmem_node_data[0] };
+struct pglist_data __refdata contig_page_data = { .bdata = &bootmem_node_data[0] };
 EXPORT_SYMBOL(contig_page_data);
 #endif