md/raid1: Add check for missing source disk in process_checks()
JIRA: https://issues.redhat.com/browse/RHEL-96672
Upstream Status: commit is found in Linus's git tree
BREW: https://brewweb.engineering.redhat.com/brew/taskinfo?taskID=67941201
Signed-off-by: Nigel Croxon ncroxon@redhat.com