s390/ptrace: add missing linux/const.h include

Adrian Reber reported the following CRIU build bug after
commit b8af5999

 ("s390/ptrace: make all psw related
defines also available for asm"):

compel/arch/s390/src/lib/infect.c: In function 'arch_can_dump_task':
compel/arch/s390/src/lib/infect.c:523:25: error: 'UL' undeclared (first use in this function)
  523 |         if (psw->mask & PSW_MASK_RI) {
      |                         ^~~~~~~~~~~

Add the missing linux/const.h include to fix this.

Reported-by: Adrian Reber <areber@redhat.com>
Closes: https://bugzilla.redhat.com/show_bug.cgi?id=2225745
Link: https://github.com/checkpoint-restore/criu/pull/2232
Tested-by: Adrian Reber <areber@redhat.com>
Fixes: b8af5999

 ("s390/ptrace: make all psw related defines also available for asm")
Link: https://lore.kernel.org/r/20230731183926.330932-1-hca@linux.ibm.com
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>