fscrypt: switch from ->is_encrypted() to IS_ENCRYPTED()

IS_ENCRYPTED() now gives the same information as
i_sb->s_cop->is_encrypted() but is more efficient, since IS_ENCRYPTED()
is just a simple flag check.  Prepare to remove ->is_encrypted() by
switching all callers to IS_ENCRYPTED().

Acked-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
diff --git a/fs/crypto/crypto.c b/fs/crypto/crypto.c
index c7835df..608f6bb 100644
--- a/fs/crypto/crypto.c
+++ b/fs/crypto/crypto.c
@@ -340,7 +340,7 @@
 		return -ECHILD;
 
 	dir = dget_parent(dentry);
-	if (!d_inode(dir)->i_sb->s_cop->is_encrypted(d_inode(dir))) {
+	if (!IS_ENCRYPTED(d_inode(dir))) {
 		dput(dir);
 		return 0;
 	}