net: bcmgenet: request and enable main clock earlier

bcmgenet_set_hw_params() will read the hardware version and compare it
with the one we are getting from Device Tree. Due to the clock being
enabled too late, bcmgenet_set_hw_params() will cause bus errors since
the GENET hardware block is still gated off by the time
bcmgenet_set_hw_params() is called, this will also make us fail the
version check since we will read the value 0 from the hardware.

Fix this by requesting the clock before the first piece of code that
needs to access hardware register.

Fixes: 1c1008c7 ("net: bcmgenet: add main driver file")
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>