[PATCH] check_partition(): fix error check

Fix inverted check introduced in 57881dd9

 "Fix
check_partition routines".

Signed-off-by: Suzuki K P <suzuki@in.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>