audit: fix typo in auditfilter.c comment

Correct the misspelling of "searching" (was "serarching")
in the function documentation for audit_update_lsm_rules.

Found via code inspection, no functional impact.

Signed-off-by: Kieran Moy <kfatyuip@gmail.com>
Signed-off-by: Paul Moore <paul@paul-moore.com>