ssb: Fix error return code in ssb_bus_scan()

Fix to return -EINVAL from the error handling case instead of 0, as done
elsewhere in this function.

Fixes: 61e115a5 ("[SSB]: add Sonics Silicon Backplane bus support")
Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: Zhen Lei <thunder.leizhen@huawei.com>
Acked-by: Michael Büsch <m@bues.ch>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/20210515072949.7151-1-thunder.leizhen@huawei.com