staging: et131x: Replace magic numbers in et1310_phy.c with defines

Replaced et131x_phy.c magic numbers specifying registers and their values with defines, defined in et131x_phy.h

Signed-off-by: Mark Einon <mark.einon@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>