net: ftgmac100: access hardware register after clock ready

net: ftgmac100: access hardware register after clock ready

BugLink: https://bugs.launchpad.net/bugs/1969857
[ Upstream commit 3d2504524531990b32a0629cc984db44f399d161 ]

AST2600 MAC register 0x58 is writable only when the MAC clock is
enabled.  Usually, the MAC clock is enabled by the bootloader so
register 0x58 is set normally when the bootloader is involved.  To make
ast2600 ftgmac100 work without the bootloader, postpone the register
write until the clock is ready.

Fixes: 137d23cea1c0 ("net: ftgmac100: Fix Aspeed ast2600 TX hang issue")
Signed-off-by: Dylan Hung <dylan_hung@aspeedtech.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>