power: pmic: tps65218: Fix tps65218_voltage_update function

Currently while setting the vsel value for dcdc1 and dcdc2
the driver is wrongly masking the entire 8 bits in the process
clearing PFM (bit7) field as well. Hence describe an appropriate
mask for vsel field and modify only those bits in the vsel
mask.

Source: http://www.ti.com/lit/ds/symlink/tps65218.pdf

Signed-off-by: Keerthy <j-keerthy@ti.com>
Fixes: 86db550b38 ("power: Add support for the TPS65218 PMIC")
Reviewed-by: Jaehoon Chung <jh80.chung@samsung.com>
diff --git a/include/power/tps65218.h b/include/power/tps65218.h
index 4d68faa..e3538e2 100644
--- a/include/power/tps65218.h
+++ b/include/power/tps65218.h
@@ -56,6 +56,8 @@
 
 #define TPS65218_MASK_ALL_BITS			0xFF
 
+#define TPS65218_DCDC_VSEL_MASK			0x3F
+
 #define TPS65218_DCDC_VOLT_SEL_0950MV		0x0a
 #define TPS65218_DCDC_VOLT_SEL_1100MV		0x19
 #define TPS65218_DCDC_VOLT_SEL_1200MV		0x23