mm: zbud: fix condition check on allocation size

mm: zbud: fix condition check on allocation size

zbud_alloc() incorrectly verifies the size of allocation limit.  It should
deny the allocation request greater than (PAGE_SIZE - ZHDR_SIZE_ALIGNED -
CHUNK_SIZE), not (PAGE_SIZE - ZHDR_SIZE_ALIGNED) which has no remaining
spaces for its buddy.  There is no point in spending the entire zbud page
storing only a single page, since we don't have any benefits.

Signed-off-by: Heesub Shin <heesub.shin@samsung.com>
Acked-by: Seth Jennings <sjenning@linux.vnet.ibm.com>
Cc: Bob Liu <bob.liu@oracle.com>
Cc: Dongjun Shin <d.j.shin@samsung.com>
Cc: Sunae Seo <sunae.seo@samsung.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>