s390/uapi: correct whitespace & coding style in asm/ptrace.h

Correct whitespace and coding style issues in the s390 asm/ptrace.h
uapi header file.  This is preparatory work to copy it to the tools/
directory for inclusion by selftests and perf.

Signed-off-by: Hendrik Brueckner <brueckner@linux.vnet.ibm.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>