net: pcs: xpcs: fix incorrect number of interfaces

In synopsys_xpcs_compat[], the DW_XPCS_2500BASEX entry was setting
the number of interfaces using the xpcs_2500basex_features array
rather than xpcs_2500basex_interfaces. This causes us to overflow
the array of interfaces. Fix this.

Fixes: f27abde3 ("net: pcs: add 2500BASEX support for Intel mGbE controller")
Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Reviewed-by: Leon Romanovsky <leonro@nvidia.com>
Signed-off-by: David S. Miller <davem@davemloft.net>