net/faraday: Add missing include of of.h

[ Upstream commit d39004ab136ebb6949a7dda9d24376f3d6209295 ]

Breaking the include loop netdevice.h, dsa.h, devlink.h broke this
driver, it depends on includes brought in by these headers. Adding
linux/of.h fixes it.

Fixes: ed0e39e97d34 ("net: break include loop netdevice.h, dsa.h, devlink.h")
Signed-off-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>