net: stmmac: Return early if invalid in loongson_dwmac_fix_reset()

net: stmmac: Return early if invalid in loongson_dwmac_fix_reset()

If the MAC controller does not connect to any PHY interface, there is a
missing clock, then the DMA reset fails.

For this case, the DMA_BUS_MODE_SFT_RESET bit is 1 before software reset,
just print an error message which gives a hint the PHY clock is missing,
and then return -EINVAL immediately to avoid waiting for the timeout when
the DMA reset fails in loongson_dwmac_fix_reset().

With this patch, for the normal end user, the computer start faster with
reducing boot time for 2 seconds on the specified mainboard.

Signed-off-by: Tiezhu Yang <yangtiezhu@loongson.cn>
Link: https://patch.msgid.link/20250811073506.27513-4-yangtiezhu@loongson.cn
Signed-off-by: Jakub Kicinski <kuba@kernel.org>