net: pcs: xpcs: pass xpcs instead of xpcs->id to xpcs_find_compat()

xpcs_find_compat() is now always passed xpcs->id. Rather than always
dereferencing this in the caller, move it into xpcs_find_compat(),
thus making this function consistent with most of the other xpcs
functions in taking an xpcs pointer.

Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Signed-off-by: David S. Miller <davem@davemloft.net>