clk: clk-wm831x: fix a logic error

clk: clk-wm831x: fix a logic error

BugLink: http://bugs.launchpad.net/bugs/1655969
commit 20979202ee6e4c68dab7bcf408787225a656d18e upstream.

Fix bug https://bugzilla.kernel.org/show_bug.cgi?id=188561. Function
wm831x_clkout_is_prepared() returns "true" when it fails to read
CLOCK_CONTROL_1. "true" means the device is already prepared. So
return "true" on the read failure seems improper.

Signed-off-by: Pan Bian <bianpan2016@163.com>
Acked-by: Charles Keepax <ckeepax@opensource.wolfsonmicro.com>
Fixes: f05259a6ffa4 ("clk: wm831x: Add initial WM831x clock driver")
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Tim Gardner <tim.gardner@canonical.com>
Signed-off-by: Luis Henriques <luis.henriques@canonical.com>