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.

Signed-off-by: Venkat Gopalakrishnan <venkatg@codeaurora.org>
Signed-off-by: Ritesh Harjani <riteshh@codeaurora.org>
Tested-by: Jeremy McNicoll <jeremymc@redhat.com>
Acked-by: Adrian Hunter <adrian.hunter@intel.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>