LoongArch: Remove dead code in relocate_new_kernel

The initial aim is to silence the following objtool warning:

arch/loongarch/kernel/relocate_kernel.o: warning: objtool: relocate_new_kernel+0x74: unreachable instruction

There are two adjacent "b" instructions, the second one is unreachable,
it is dead code, just remove it.

Co-developed-by: Jinyang He <hejinyang@loongson.cn>
Signed-off-by: Jinyang He <hejinyang@loongson.cn>
Co-developed-by: Youling Tang <tangyouling@loongson.cn>
Signed-off-by: Youling Tang <tangyouling@loongson.cn>
Signed-off-by: Tiezhu Yang <yangtiezhu@loongson.cn>
Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>