clk: qcom: clk-debug: Fix accessing mux when it is NULL

When debugcc did not register, measure/mux will be NULL.
Avoid accessing it.

Change-Id: I037151e258ae85c89c9db87254e5b8ea850157a0
Signed-off-by: Veera Vegivada <quic_vvegivad@quicinc.com>

drivers/clk/qcom/clk-debug.c

@@ -445,6 +445,9 @@ static int clk_debug_measure_get(void *data, u64 *val)
 	int ret = 0;
 	u32 regval;
 
+	if (!measure)
+		return -EINVAL;
+
 	ret = clk_runtime_get_debug_mux(meas);
 	if (ret)
 		return ret;