lan78xx: select CRC32

Fix the following build/link error by adding a dependency on the CRC32
routines:

  ld: drivers/net/usb/lan78xx.o: in function `lan78xx_set_multicast':
  lan78xx.c:(.text+0x48cf): undefined reference to `crc32_le'

The actual use of crc32_le() comes indirectly through ether_crc().

Fixes: 55d7de9d ("Microchip's LAN7800 family USB 2/3 to 10/100/1000 Ethernet device driver")
Signed-off-by: Vegard Nossum <vegard.nossum@oracle.com>
Signed-off-by: David S. Miller <davem@davemloft.net>