scsi: ufs-msm: disable the sigdet before power collapsing PHY

If UFS PHY power down is deasserted and power is restored to analog
circuits, the rx_sigdet can glitch. If the glitch is wide enough,
it can trigger the PHY digital logic to think it saw a DIF-N and
cause it to exit Hibern8. Disabling the rx_sigdet during power-up
will mask the glitch.

Change-Id: I20d93d2f5b479bb9e1d9626cfb9939d280b172a5
Signed-off-by: Subhash Jadavani <subhashj@codeaurora.org>