USB: Fix signr comment in usbdevice_fs.h

This trivial documentation patch corrects a comment in usbdevice_fs.h; it
previously suggested that the signal would only be sent on error, but I am
told that it is sent on both successful and unsuccessful completion, and
that zero indicates that no signal should be sent.
Signed-off-by: NPhil Endecott <spam_from_usb_devel@chezphil.org>
Signed-off-by: NGreg Kroah-Hartman <gregkh@suse.de>

include/linux/usbdevice_fs.h

@@ -102,7 +102,8 @@ struct usbdevfs_urb {
 	int start_frame;
 	int number_of_packets;
 	int error_count;
-	unsigned int signr;  /* signal to be sent on error, -1 if none should be sent */
+	unsigned int signr;	/* signal to be sent on completion,
+				  or 0 if none should be sent. */
 	void *usercontext;
 	struct usbdevfs_iso_packet_desc iso_frame_desc[0];
 };