docs: fix link s390/zfcpdump.rst

After move of Documentation/s390 to Documentation/arch/s390

Link: https://lkml.kernel.org/r/20230825013102.1487979-1-costa.shul@redhat.com


Signed-off-by: Costa Shulyupin <costa.shul@redhat.com>
Cc: Baoquan He <bhe@redhat.com>
Cc: Eric DeVolder <eric.devolder@oracle.com>
Cc: Hari Bathini <hbathini@linux.ibm.com>
Cc: Sourabh Jain <sourabhjain@linux.ibm.com>
Cc: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>