ima: fix cred sparse warning

Fix ima_policy.c sparse "warning: dereference of noderef expression"
message, by accessing cred->uid using current_cred().

Changelog v1:
- Change __cred to just cred (based on David Howell's comment)
Signed-off-by: Mimi Zohar <zohar@us.ibm.com>
Signed-off-by: James Morris <jmorris@namei.org>

security/integrity/ima/ima_policy.c

@@ -99,6 +99,7 @@ static bool ima_match_rules(struct ima_measure_rule_entry *rule,
 			    struct inode *inode, enum ima_hooks func, int mask)
 {
 	struct task_struct *tsk = current;
+	const struct cred *cred = current_cred();
 	int i;
 
 	if ((rule->flags & IMA_FUNC) && rule->func != func)
@@ -108,7 +109,7 @@ static bool ima_match_rules(struct ima_measure_rule_entry *rule,
 	if ((rule->flags & IMA_FSMAGIC)
 	    && rule->fsmagic != inode->i_sb->s_magic)
 		return false;
-	if ((rule->flags & IMA_UID) && rule->uid != tsk->cred->uid)
+	if ((rule->flags & IMA_UID) && rule->uid != cred->uid)
 		return false;
 	for (i = 0; i < MAX_LSM_RULES; i++) {
 		int rc = 0;