mtd: nand: fix multi-chip suspend problem

Symptom:
device_suspend(): mtd_cls_suspend+0x0/0x58 returns -11
PM: Device mtd14 failed to suspend: error -11
PM: Some devices failed to suspend

This patch enables other chips to be suspended if the active chip of
the controller has been suspended.

Signed-off-by: Jin Qing <b24347@freescale.com>
Signed-off-by: Li Yang <leoli@freescale.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>