powerpc: remove unneeded semicolon

Fix the following coccicheck warnings:

./arch/powerpc/kernel/prom_init.c:2986:2-3: Unneeded semicolon.

Reported-by: Abaci Robot <abaci@linux.alibaba.com>
Signed-off-by: Jiapeng Chong <jiapeng.chong@linux.alibaba.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/1614151761-53721-1-git-send-email-jiapeng.chong@linux.alibaba.com