types: s390: fix #ifdef reversal in <asm-s390/types.h>

The #ifdef for the integer types was reversed; the standard pattern in
these files are:

#ifndef __s390x__
/* 32-bit code */
#else
/* 64-bit code */
#endif

Stick with the original pattern, but make sure the 32-bit code
actually comes first!

Reported by Al Viro.

Signed-off-by: H. Peter Anvin <hpa@zytor.com>
Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
Cc: Heiko Carstens <heiko.carstens@de.ibm.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>