net: bgmac: postpone turning IRQs off to avoid SoC hangs

Turning IRQs off is done by accessing Ethernet controller registers.
That can't be done until device's clock is enabled. It results in a SoC
hang otherwise.

This bug remained unnoticed for years as most bootloaders keep all
Ethernet interfaces turned on. It seems to only affect a niche SoC
family BCM47189. It has two Ethernet controllers but CFE bootloader uses
only the first one.

Fixes: 34322615 ("net: bgmac: Mask interrupts during probe")
Signed-off-by: Rafał Miłecki <rafal@milecki.pl>
Reviewed-by: Michal Kubiak <michal.kubiak@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>