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

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/[email protected]
Signed-off-by: Richard Leitner <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>