staging: mt7621-mmc: Refactor and rename msdc_reset to msdc_reset_hw

In the current code the hardware reset is realised via a macro and
does only wait for a certain ammount of time for the controller to
come out of reset state, but it should wait until it IS out of reset
state. So it is refactored to improve this, it is also changed from a
macro to a function and renamed to msdc_reset_hw to match the mtk-sd
driver.

Signed-off-by: Christian Lütke-Stetzkamp <christian@lkamp.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>