Fix a typo in impedance setting for ethernet-phy@3

Fixes: b76db38c ("ARM: dts: dra72-evm-revc: add phy impedance settings")
Cc: Mugunthan V N <mugunthanvnm@ti.com>
Signed-off-by: Sekhar Nori <nsekhar@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>