clk: mxs: fix ref_io clock definition

The definition of clocks ref_io0 and ref_io1 were inverted.  It causes
a mmc regression on some boards right away.  Fix the regression by
correcting the ref_io clock definition.

Reported-by: Maxime Ripard <maxime.ripard@free-electrons.com>
Signed-off-by: Shawn Guo <shawn.guo@linaro.org>
Signed-off-by: Mike Turquette <mturquette@linaro.org>