ima_setup.sh: Add digest index detection for ima-buf format

"ima-buf" will be used in following commit "IMA: Read required policy from file".

Link: https://lore.kernel.org/ltp/20250114112915.610297-8-pvorel@suse.cz/
Reviewed-by: Mimi Zohar <zohar@linux.ibm.com>
Signed-off-by: Petr Vorel <pvorel@suse.cz>

Author: pevik

testcases/kernel/security/integrity/ima/tests/ima_setup.sh

@@ -209,7 +209,7 @@ set_digest_index()
 	# parse digest index
 	# https://www.kernel.org/doc/html/latest/security/IMA-templates.html#use
 	case "$template" in
-	ima|ima-ng|ima-sig) DIGEST_INDEX=4 ;;
+	ima|ima-buf|ima-ng|ima-sig) DIGEST_INDEX=4 ;;
 	*)
 		# using ima_template_fmt kernel parameter
 		local IFS="|"