net: phy: mxl-gpy: correctly describe LED polarity

According the datasheet covering the LED (0x1b) register:
0B Active High LEDx pin driven high when activated
1B Active Low LEDx pin driven low when activated

Make use of the now available 'active-high' property and correctly
reflect the polarity setting which was previously inverted.

Signed-off-by: Daniel Golle <daniel@makrotopia.org>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Link: https://patch.msgid.link/180ccafa837f09908b852a8a874a3808c5ecd2d0.1728558223.git.daniel@makrotopia.org


Signed-off-by: Paolo Abeni <pabeni@redhat.com>