s390/relocate_kernel: adjust indentation

relocate_kernel.S seems to be the only assembler file which doesn't
follow the standard way of indentation. Adjust this for the sake of
consistency.

Signed-off-by: Heiko Carstens <hca@linux.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>