ALSA: usb-audio: Fix invalid NULL check in snd_emuusb_set_samplerate()

BugLink: https://bugs.launchpad.net/bugs/1885932

commit 6de3c9e3 upstream.

The quirk function snd_emuusb_set_samplerate() has a NULL check for
the mixer element, but this is useless in the current code.  It used
to be a check against mixer->id_elems[unitid] but it was changed later
to the value after mixer_eleme_list_to_info() which is always non-NULL
due to the container_of() usage.

This patch fixes the check before the conversion.

While we're at it, correct a typo in the comment in the function,
too.

Fixes: 8c558076 ("ALSA: usb-audio: Clean up mixer element list traverse")
Cc: <stable@vger.kernel.org>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
Signed-off-by: Kelsey Skunberg <kelsey.skunberg@canonical.com>

sound/usb/mixer_quirks.c

@@ -1168,18 +1168,18 @@ void snd_emuusb_set_samplerate(struct snd_usb_audio *chip,
 {
 	struct usb_mixer_interface *mixer;
 	struct usb_mixer_elem_info *cval;
-	int unitid = 12; /* SamleRate ExtensionUnit ID */
+	int unitid = 12; /* SampleRate ExtensionUnit ID */
 
 	list_for_each_entry(mixer, &chip->mixer_list, list) {
+		if (mixer->id_elems[unitid]) {
 			cval = mixer_elem_list_to_info(mixer->id_elems[unitid]);
-		if (cval) {
 			snd_usb_mixer_set_ctl_value(cval, UAC_SET_CUR,
 						    cval->control << 8,
 						    samplerate_id);
 			snd_usb_mixer_notify_id(mixer, unitid);
-		}
 			break;
 		}
+	}
 }
 
 /* M-Audio Fast Track C400/C600 */