staging: mt7621-mmc: Remove function uffs

The function uffs that is implemented by this driver returns the same
values as the kernel function ffs. So the uffs function is removed and
the calls to it are replaced with calls to ffs.

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