mmc: sdhci-msm: Reset vendor specific func register on probe

The vendor specific func register doesn't get reset when using the
software reset register. The various bootloader's could leave this
in an unknown state, hence reset this register to it's power on reset
value during probe.

Change-Id: I3258eedf87b1bc945f43b85627948e6c92b74686
Signed-off-by: Venkat Gopalakrishnan <venkatg@codeaurora.org>