mfd: Set tps6586x bits if new value is different from the old one

It does not make sense to write new value only when all the bit_mask
bits are zero.
We need to write new value if the bit mask fields of new value is
not equal to old value.
Signed-off-by: Axel Lin <axel.lin@gmail.com>
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>

drivers/mfd/tps6586x.c

@@ -197,7 +197,7 @@ int tps6586x_set_bits(struct device *dev, int reg, uint8_t bit_mask)
 	if (ret)
 		goto out;
 
-	if ((reg_val & bit_mask) == 0) {
+	if ((reg_val & bit_mask) != bit_mask) {
 		reg_val |= bit_mask;
 		ret = __tps6586x_write(to_i2c_client(dev), reg, reg_val);
 	}