refactor(drivers/marvell/comphy-3700): rename Digital Loopback Enable register constant

The register at offset 0x23 is called Digital Loopback Enable, but the
constant is COMPHY_LOOPBACK_REG0, as if there were some LOOPBACK_REG1
register or something, which there is not.

Rename the constant to COMPHY_DIG_LOOPBACK_EN.

Signed-off-by: Marek Behún <marek.behun@nic.cz>
Change-Id: Ie88bdd864e2c9ab7e8de70ed7f3a13ee8f08ff79
diff --git a/drivers/marvell/comphy/phy-comphy-3700.h b/drivers/marvell/comphy/phy-comphy-3700.h
index 42d4a80..df89da9 100644
--- a/drivers/marvell/comphy/phy-comphy-3700.h
+++ b/drivers/marvell/comphy/phy-comphy-3700.h
@@ -75,8 +75,9 @@
 #define COMPHY_RESERVED_REG		0x0E
 #define PHYCTRL_FRM_PIN_BIT		BIT(13)
 
-#define COMPHY_LOOPBACK_REG0		0x23
-#define DIG_LB_EN_ADDR(unit)		(COMPHY_LOOPBACK_REG0 * PHY_SHFT(unit))
+#define COMPHY_DIG_LOOPBACK_EN		0x23
+#define DIG_LOOPBACK_EN_ADDR(unit)	(COMPHY_DIG_LOOPBACK_EN * \
+					 PHY_SHFT(unit))
 #define SEL_DATA_WIDTH_OFFSET		10
 #define SEL_DATA_WIDTH_MASK		(0x3 << SEL_DATA_WIDTH_OFFSET)
 #define DATA_WIDTH_10BIT		(0x0 << SEL_DATA_WIDTH_OFFSET)