mm/memblock.c: remove unnecessary always-true comparison

Comparing an u64 variable to >= 0 returns always true and can therefore
be removed.  This issue was detected using the -Wtype-limits gcc flag.

This patch fixes following type-limits warning:

  mm/memblock.c: In function `__next_reserved_mem_region':
  mm/memblock.c:843:11: warning: comparison of unsigned expression >= 0 is always true [-Wtype-limits]
    if (*idx >= 0 && *idx < type->cnt) {

Link: http://lkml.kernel.org/r/20160510103625.3a7f8f32@g0hl1n.net
Signed-off-by: Richard Leitner <dev@g0hl1n.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/memblock.c

@@ -824,7 +824,7 @@ void __init_memblock __next_reserved_mem_region(u64 *idx,
 {
 	struct memblock_type *type = &memblock.reserved;
 
-	if (*idx >= 0 && *idx < type->cnt) {
+	if (*idx < type->cnt) {
 		struct memblock_region *r = &type->regions[*idx];
 		phys_addr_t base = r->base;
 		phys_addr_t size = r->size;