net: fix ks8851 build errors

Fix build errors due to missing Kconfig select of CRC32:

ks8851.c:(.text+0x7d2ee): undefined reference to `crc32_le'
ks8851.c:(.text+0x7d2f5): undefined reference to `bitrev32'

Signed-off-by: Randy Dunlap <randy.dunlap@oracle.com>
Signed-off-by: David S. Miller <davem@davemloft.net>