mmc: dw_mmc: Keep vqmmc-supply enable count in balance

mmc: dw_mmc: Keep vqmmc-supply enable count in balance

With the commit 4fcba5d556b4 ("regulator: implement basic reference
counter"), keeping regulator enablement in balance become more important.

Disable vqmmc-supply before signal voltage is changed to keep regulator
enable counter in balance.

Signed-off-by: Jonas Karlman <jonas@kwiboo.se>
[backport of the commit 01b2917a1973b804338d3edbbd46198c540ba9f5 from mainline]
Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
Change-Id: Ibd99b3b236906554c5ed17d5b1564f1fd0fc00fe