clk: wm831x: Fix wm831x_clkout_get_parent

Current code looks strange because calling wm831x_clkout_set_parent() with 0 as
parent parameter, wm831x_clkout_get_parent() will return 1.

According to the datasheet:
R16528 (4090h) Clock Control1
        BIT 0: CLKOUT output source select
                0 = FLL output
                1 = 32.768kHz oscillator

Thus fix the entry order in wm831x_clkout_parents[] to make it has
the same meaning as the datasheet and make the return value
of wm831x_clkout_get_parent() consistent with the parent pass to
wm831x_clkout_set_parent().

Signed-off-by: Axel Lin <axel.lin@ingics.com>
Acked-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
Signed-off-by: Mike Turquette <mturquette@linaro.org>