net: ethernet: fs-enet: Use generic CRC32 implementation

Use generic kernel CRC32 implementation because it:
1. Should be faster (uses lookup tables),
2. Removes duplicated CRC generation code,
3. Uses well-proven algorithm instead of coding it one more time.

Suggested-by: Eric Biggers <ebiggers3@gmail.com>
Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>