MIPS: Sibyte: remove unnecessary return variable

Fix the following coccicheck warning:

arch/mips/sibyte/bcm1480/setup.c:37:5-8: Unneeded variable: "ret".
Return "0" on line 67.

Signed-off-by: Guo Zhengkui <guozhengkui@vivo.com>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>