net/phy: fix DP83865 10 Mbps HDX loopback disable function

[ Upstream commit e47488b2df7f9cb405789c7f5d4c27909fc597ae ]

According to the DP83865 datasheet "the 10 Mbps HDX loopback can be
disabled in the expanded memory register 0x1C0.1". The driver erroneously
used bit 0 instead of bit 1.

Fixes: 4621bf12 ("phy: Add file missed in previous commit.")
Signed-off-by: Peter Mamonov <pmamonov@gmail.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>