ima: sparse fix: make ima_open_policy static

Fixes sparse warning:
security/integrity/ima/ima_fs.c:290:5: warning: symbol 'ima_open_policy' was not declared. Should it be static?
Signed-off-by: James Morris <jmorris@namei.org>

security/integrity/ima/ima_fs.c

@@ -287,7 +287,7 @@ static atomic_t policy_opencount = ATOMIC_INIT(1);
 /*
  * ima_open_policy: sequentialize access to the policy file
  */
-int ima_open_policy(struct inode * inode, struct file * filp)
+static int ima_open_policy(struct inode * inode, struct file * filp)
 {
 	/* No point in being allowed to open it if you aren't going to write */
 	if (!(filp->f_flags & O_WRONLY))