clk: use uninitialized_var instead setting 'flags' to 0 directly.

Setting 'flags' to zero will be certainly a misleading way to avoid
warning of 'flags' may be used uninitialized. uninitialized_var is
a correct way because the warning is a false possitive.

Signed-off-by: Xiubo Li <Li.Xiubo@freescale.com>
Signed-off-by: Mike Turquette <mturquette@linaro.org>