mm/nobootmem.c: add return value check in __alloc_memory_core_early()

When memblock_reserve() fails because memblock.reserved.regions cannot
be resized, the caller (e.g.  alloc_bootmem()) is not informed of the
failed allocation.  Therefore alloc_bootmem() silently returns the same
pointer again and again.

This patch adds a check for the return value of memblock_reserve() in
__alloc_memory_core().

Signed-off-by: Philipp Hachtmann <phacht@linux.vnet.ibm.com>
Reviewed-by: Tejun Heo <tj@kernel.org>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Tang Chen <tangchen@cn.fujitsu.com>
Cc: Toshi Kani <toshi.kani@hp.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>