TI DaVinci EMAC: Handle emac module clock correctly.

In the driver probe function the emac module clock needs to
be enabled before calling register_netdev(). As soon as the
device is registered the driver get_stats function can be invoked
by the core - the module clock must be switched on to be able to
read from stats registers. Also explicitly call matching clk_disable
for failure conditions in probe function.

Signed-off-by: Sriramakrishnan <srk@ti.com>
Signed-off-by: David S. Miller <davem@davemloft.net>