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
2 files changed