net: dsa: bcm_sf2: factor interrupt disabling in a function

Factor the interrupt disabling in a function: bcm_sf2_intr_disable()
since we are doing the same thing in the setup and suspend paths.

Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>