clk: qcom: Check return value using correct data type

of_get_clk_src will contain an error value in case
the clk_get returns eprobe defer. Check for the correct
return value.

Change-Id: I0b40f6714cc55e1ad897280946d2964feb2410e0
Signed-off-by: Taniya Das <tdas@codeaurora.org>