mvneta: Fix hang when loading the mvneta driver

When the mvneta driver is compiled, it'll be loaded with clocks disabled.
This implies that the clocks should be enabled again before any register
access or it'll hang.

To fix it:
- enable clock earlier
- move timer callback after setting timer.data

Signed-off-by: Arnaud Patard <arnaud.patard@rtp-net.org>
Signed-off-by: David S. Miller <davem@davemloft.net>