lan78xx: remove redundant initialization of pointer 'phydev'

Pointer phydev is initialized and this value is never read, phydev
is immediately updated to a new value, hence this initialization
is redundant and can be removed

Cleans up clang warning:
drivers/net/usb/lan78xx.c:2009:21: warning: Value stored to 'phydev'
during its initialization is never read

Signed-off-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: David S. Miller <davem@davemloft.net>