net/mlx4_core: Unmap UAR also in the case of error flow

If a failure takes place during the EQ creation, we need to unmap the
UAR memory block too.

Signed-off-by: Dotan Barak <dotanb@dev.mellanox.co.il>
Signed-off-by: Uri Habusha <urih@mellanox.com>
Signed-off-by: Or Gerlitz <ogerlitz@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>