pwm: imx: Prevent NULL pointer dereference

pwm_id_to_reg() can return NULL, so add NULL testing to prevent NULL pointer
dereference.

Signed-off-by: Axel Lin <axel.lin@ingics.com>
Acked-by: Stefano Babic <sbabic@denx.de>
Acked-by: Heiko Schocher <hs@denx.de>

drivers/pwm/pwm-imx.c

@@ -18,6 +18,9 @@ int pwm_init(int pwm_id, int div, int invert)
 {
 	struct pwm_regs *pwm = (struct pwm_regs *)pwm_id_to_reg(pwm_id);
 
+	if (!pwm)
+		return -1;
+
 	writel(0, &pwm->ir);
 	return 0;
 }
@@ -28,6 +31,9 @@ int pwm_config(int pwm_id, int duty_ns, int period_ns)
 	unsigned long period_cycles, duty_cycles, prescale;
 	u32 cr;
 
+	if (!pwm)
+		return -1;
+
 	pwm_imx_get_parms(period_ns, duty_ns, &period_cycles, &duty_cycles,
 			  &prescale);
 
@@ -47,6 +53,9 @@ int pwm_enable(int pwm_id)
 {
 	struct pwm_regs *pwm = (struct pwm_regs *)pwm_id_to_reg(pwm_id);
 
+	if (!pwm)
+		return -1;
+
 	setbits_le32(&pwm->cr, PWMCR_EN);
 	return 0;
 }
@@ -55,5 +64,8 @@ void pwm_disable(int pwm_id)
 {
 	struct pwm_regs *pwm = (struct pwm_regs *)pwm_id_to_reg(pwm_id);
 
+	if (!pwm)
+		return;
+
 	clrbits_le32(&pwm->cr, PWMCR_EN);
 }