compat: Re-add missing asm/compat.h include to fix compile breakage on s390

compat: Re-add missing asm/compat.h include to fix compile breakage on s390

For kernels < 3.0 the backport of 048cd4e51d24ebf7f3552226d03c769d6ad91658
"compat: fix compile breakage on s390" will break compilation...

Re-add a single #include <asm/compat.h> in order to fix this.

This patch is _not_ necessary for upstream, only for stable kernels
which include the "build fix" mentioned above.

Reported-by: Jiri Slaby <jslaby@suse.cz>
Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Willy Tarreau <w@1wt.eu>