sh: initialize max_mapnr

sh never initializes max_mapnr which is used by the generic implementation
of pfn_valid().

Initialize max_mapnr with set_max_mapnr() in sh::paging_init().

Link: https://lkml.kernel.org/r/[email protected]
Fixes: e5080a9 ("mm, arch: add generic implementation of pfn_valid() for FLATMEM")
Reported-by: Guenter Roeck <[email protected]>
Signed-off-by: Mike Rapoport (IBM) <[email protected]>
Acked-by: John Paul Adrian Glaubitz <[email protected]>
Reviewed-by: David Hildenbrand <[email protected]>
Cc: Arnd Bergmann <[email protected]>
Cc: Geert Uytterhoeven <[email protected]>
Cc: Greg Ungerer <[email protected]>
Cc: Rich Felker <[email protected]>
Cc: Yoshinori Sato <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

Author: rppt

arch/sh/mm/init.c

@@ -301,6 +301,7 @@ void __init paging_init(void)
 	 */
 	max_low_pfn = max_pfn = memblock_end_of_DRAM() >> PAGE_SHIFT;
 	min_low_pfn = __MEMORY_START >> PAGE_SHIFT;
+	set_max_mapnr(max_low_pfn - min_low_pfn);
 
 	nodes_clear(node_online_map);