sunxi: correct pinmux setup

Bo Shen reported that MMC no longer worked after commit ff42704 "sunxi: use
clrsetbit in gpio/pinmux code".

Re-examining those changes shows a couple of bogus changes (forgetting to shift
the value in one, and using the offset instead of the value in another).
Presumably Bo Shen's platform uses a different MMC device to what I tested.

Signed-off-by: Ian Campbell <ijc@hellion.org.uk>
Cc: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>