net: fec: fix compile with CONFIG_M5272

Commit 80cca775 ("net: fec: cache statistics while device is down")
introduced unconditional statistics-related actions.

However, when driver is compiled with CONFIG_M5272, staticsics-related
definitions do not exist, which results into build errors.

Fix that by adding explicit handling of !defined(CONFIG_M5272) case.

Fixes: 80cca775

 ("net: fec: cache statistics while device is down")
Signed-off-by: Nikita Yushchenko <nikita.yoush@cogentembedded.com>
Signed-off-by: David S. Miller <davem@davemloft.net>