mmc: sdhci-msm: Avoid enable SD power if card is not present

Properly avoid turn on the SD card power when SD card is removed.
In some multi card tray designs, removing the SD card may cause
the SD card power supply pin to come in contact with the SIM card.
This change is to ensure the SD card power is not active when
the SD card is removed. As a result, avoid possible damage to
the SIM card in case the SD card power makes contact with
the SIM card.

Change-Id: I45a2bb434bd2bc76957ae382eecd5cce9e743918
Signed-off-by: Bao D. Nguyen <nguyenb@codeaurora.org>