driver: ddr: imx: correct the pwrctl setting of selfref_en on imx8m

The 'selfref_en' should be bit'0', so correct the setting to
enable the auto self-refresh.

Reviewed-by: Jian Li <jian.li@nxp.com>
Reviewed-by: Ye Li <ye.li@nxp.com>
Signed-off-by: Jacky Bai <ping.bai@nxp.com>
Signed-off-by: Peng Fan <peng.fan@nxp.com>
diff --git a/drivers/ddr/imx/imx8m/ddr_init.c b/drivers/ddr/imx/imx8m/ddr_init.c
index 1c5c7f9..de30293 100644
--- a/drivers/ddr/imx/imx8m/ddr_init.c
+++ b/drivers/ddr/imx/imx8m/ddr_init.c
@@ -163,7 +163,7 @@
 	/* Step26: Set back register in Step4 to the original values if desired */
 	reg32_write(DDRC_RFSHCTL3(0), 0x0000000);
 	/* enable selfref_en by default */
-	setbits_le32(DDRC_PWRCTL(0), 0x1 << 3);
+	setbits_le32(DDRC_PWRCTL(0), 0x1);
 
 	/* enable port 0 */
 	reg32_write(DDRC_PCTRL_0(0), 0x00000001);