soc: ti: pm33xx: Remove set but unused variable 'ret'

Fixes the following W=1 kernel build warning(s):

 drivers/soc/ti/pm33xx.c: In function ‘am33xx_do_sram_idle’:
 drivers/soc/ti/pm33xx.c:138:6: warning: variable ‘ret’ set but not used [-Wunused-but-set-variable]

Cc: Santosh Shilimkar <ssantosh@kernel.org>
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Signed-off-by: Santosh Shilimkar <santosh.shilimkar@oracle.com>

drivers/soc/ti/pm33xx.c

@@ -135,13 +135,11 @@ static int am33xx_push_sram_idle(void)
 
 static int am33xx_do_sram_idle(u32 wfi_flags)
 {
-	int ret = 0;
-
 	if (!m3_ipc || !pm_ops)
 		return 0;
 
 	if (wfi_flags & WFI_FLAG_WAKE_M3)
-		ret = m3_ipc->ops->prepare_low_power(m3_ipc, WKUP_M3_IDLE);
+		m3_ipc->ops->prepare_low_power(m3_ipc, WKUP_M3_IDLE);
 
 	return pm_ops->cpu_suspend(am33xx_do_wfi_sram, wfi_flags);
 }