soc: ti: pm33xx: Fix static checker warnings

The patch fixes a bunch of static checker warnings.

Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Keerthy <j-keerthy@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>

drivers/soc/ti/pm33xx.c

@@ -252,7 +252,7 @@ static int am33xx_pm_begin(suspend_state_t state)
 	if (state == PM_SUSPEND_MEM && pm_ops->check_off_mode_enable()) {
 		nvmem = devm_nvmem_device_get(&omap_rtc->dev,
 					      "omap_rtc_scratch0");
-		if (nvmem)
+		if (!IS_ERR(nvmem))
 			nvmem_device_write(nvmem, RTC_SCRATCH_MAGIC_REG * 4, 4,
 					   (void *)&rtc_magic_val);
 		rtc_only_idle = 1;
@@ -278,9 +278,12 @@ static void am33xx_pm_end(void)
 	struct nvmem_device *nvmem;
 
 	nvmem = devm_nvmem_device_get(&omap_rtc->dev, "omap_rtc_scratch0");
+	if (IS_ERR(nvmem))
+		return;
+
 	m3_ipc->ops->finish_low_power(m3_ipc);
 	if (rtc_only_idle) {
-		if (retrigger_irq)
+		if (retrigger_irq) {
 			/*
 			 * 32 bits of Interrupt Set-Pending correspond to 32
 			 * 32 interrupts. Compute the bit offset of the
@@ -291,8 +294,10 @@ static void am33xx_pm_end(void)
 			writel_relaxed(1 << (retrigger_irq & 31),
 				       gic_dist_base + GIC_INT_SET_PENDING_BASE
 				       + retrigger_irq / 32 * 4);
-			nvmem_device_write(nvmem, RTC_SCRATCH_MAGIC_REG * 4, 4,
-					   (void *)&val);
+		}
+
+		nvmem_device_write(nvmem, RTC_SCRATCH_MAGIC_REG * 4, 4,
+				   (void *)&val);
 	}
 
 	rtc_only_idle = 0;
@@ -415,7 +420,7 @@ static int am33xx_pm_rtc_setup(void)
 
 		nvmem = devm_nvmem_device_get(&omap_rtc->dev,
 					      "omap_rtc_scratch0");
-		if (nvmem) {
+		if (!IS_ERR(nvmem)) {
 			nvmem_device_read(nvmem, RTC_SCRATCH_MAGIC_REG * 4,
 					  4, (void *)&rtc_magic_val);
 			if ((rtc_magic_val & 0xffff) != RTC_REG_BOOT_MAGIC)