scsi: ufs: Don't turn of the link for WDC devices during LPM

WDC has confirmed that their device can't handle frequent power cycles.
So don't turn off the link for WDC devise when switching to low power
mode.

Change-Id: If2f438c5df025fc79051031ca2a098c48324ec22
Signed-off-by: Veerabhadrarao Badiganti <vbadigan@codeaurora.org>