media: r820t: don't crash if attach fails

As pointed by smatch:
	drivers/media/tuners/r820t.c:2374 r820t_attach() error: potential null dereference 'priv'.  (kzalloc returns null)

The current function with prints error assumes that the attach
succeeds. So, don't use it in case of failures.
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>

drivers/media/tuners/r820t.c

@@ -20,6 +20,8 @@
 //
 //	RF Gain set/get is not implemented.
 
+#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
+
 #include <linux/videodev2.h>
 #include <linux/mutex.h>
 #include <linux/slab.h>
@@ -2371,7 +2373,7 @@ struct dvb_frontend *r820t_attach(struct dvb_frontend *fe,
 err_no_gate:
 	mutex_unlock(&r820t_list_mutex);
 
-	tuner_info("%s: failed=%d\n", __func__, rc);
+	pr_info("%s: failed=%d\n", __func__, rc);
 	r820t_release(fe);
 	return NULL;
 }