8139cp/8139too: do not read into reserved registers

delay_eeprom() use long read for Cfg9346 register(offset 0x50) which may read
into the area of reserved register(offset 0x53). Use byte read instead.

Signed-off-by: Jason Wang <jasowang@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>