net: phy: at803x: fix coccinelle warnings

drivers/net/phy/at803x.c:196:26-32: ERROR: application of sizeof to pointer

 sizeof when applied to a pointer typed expression gives the size of
 the pointer

Generated by: scripts/coccinelle/misc/noderef.cocci

Signed-off-by: Fengguang Wu <fengguang.wu@intel.com>
Acked-by: Daniel Mack <zonque@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>