apparmor: fix spelling mistake "immutible" -> "immutable"

There is a spelling mistake in an information message string, fix it.
Signed-off-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: John Johansen <john.johansen@canonical.com>

security/apparmor/policy.c

@@ -587,7 +587,7 @@ static int replacement_allowed(struct aa_profile *profile, int noreplace,
 {
 	if (profile) {
 		if (profile->label.flags & FLAG_IMMUTIBLE) {
-			*info = "cannot replace immutible profile";
+			*info = "cannot replace immutable profile";
 			return -EPERM;
 		} else if (noreplace) {
 			*info = "profile already exists";