LoongArch: Fix disassembly option parsing stopping at the first option

LoongArch: Fix disassembly option parsing stopping at the first option

Turns out the return value of parse_loongarch_dis_option acts as an
error code, and previously the function always signified failure with
a non-zero return value, making only the first disassembly option get
to take effect.

Fix by adding the missing `return 0`'s to the two success code paths.

Signed-off-by: WANG Xuerui <git@xen0n.name>