mmc: core: abort rescan if suspend is triggered

There could be a race between suspend and mmc_rescan as follows:
At resume:
-> mmc_pm_notify
  -> mmc_rescan is scheduled

Suspend is triggered:
-> mmc_pm_notify
   -> wait for mmc_rescan/cancel it
      -> rescan acquires wakelock if card is detected
         so as to give user-space a chance to respond
-> PM framework cancels suspend since wakelock is active

Hence, release the wake-lock if its active in suspend prepare
and check for rescan_disable before acquiring wake-lock.
This prefers suspend over notifying the user-space of the status
of the card, which is fine since with suspend user-space is frozen
too.

CRs-fixed: 655281
Change-Id: I83783589f9b541d3af73931e9a7b0b144a25538e
Signed-off-by: Asutosh Das <asutoshd@codeaurora.org>