net: zynq_gem: Fix masking of supported phydev features

When the zynq_gem driver initializes the phy it sets the supported
features that the phy can support and advertise. However instead of
masking the supported features such that it limits the available
features it sets the phy to have the exact supported features of the
zynq_gem. This is problematic as it will enable features that a phy does
not have or cannot advertise.

Specifically this appears as an issue when using a phy that is only
capable of 10/100, but the zynq_gem driver will override this and try to
enable and advertise 10/100/1000.

Reported-by: Arno Steffens <star@gmx.li>
Fixes: 80243528 ("net: gem: Fix gem driver on 1Gbps LAN")
Signed-off-by: Nathan Rossi <nathan@nathanrossi.com>
Tested-by: Arno Steffens <star@gmx.li>
Cc: Joe Hershberger <joe.hershberger@ni.com>
Cc: Michal Simek <michal.simek@xilinx.com>
Acked-by: Joe Hershberger <joe.hershberger@ni.com>
Acked-by: Michal Simek <michal.simek@xilinx.com>