ARM: OMAP4: MMC: no regulator off during probe for eMMC

eMMC does not handle power off when not in sleep state,
Skip regulator disable during probe when eMMC is
not in known state - state left by bootloader.

Resolves eMMC failure on OMAP4
mmc0: error -110 whilst initialising MMC card

Signed-off-by: Balaji T K <balajitk@ti.com>
Tested-by: Kishore Kadiyala <kishore.kadiyala@ti.com>
Acked-by: Kishore Kadiyala <kishore.kadiyala@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>