ssb: remove unreachable code

Clean up the following smatch warning:

drivers/ssb/pci.c:917 ssb_pci_sprom_get() warn: ignoring unreachable
code.

Reported-by: Abaci Robot <abaci@linux.alibaba.com>
Signed-off-by: Jiapeng Chong <jiapeng.chong@linux.alibaba.com>
Acked-by: Michael Büsch <m@bues.ch>
Signed-off-by: Kalle Valo <kvalo@kernel.org>
Link: https://lore.kernel.org/r/20220506075814.115059-1-jiapeng.chong@linux.alibaba.com