usb: deprecate the third argument of usb_maxpacket()

This is a transitional patch with the ultimate goal of changing the
prototype of usb_maxpacket() from:
| static inline __u16
| usb_maxpacket(struct usb_device *udev, int pipe, int is_out)

into:
| static inline u16 usb_maxpacket(struct usb_device *udev, int pipe)

The third argument of usb_maxpacket(): is_out gets removed because it
can be derived from its second argument: pipe using
usb_pipeout(pipe). Furthermore, in the current version,
ubs_pipeout(pipe) is called regardless in order to sanitize the is_out
parameter.

In order to make a smooth change, we first deprecate the is_out
parameter by simply ignoring it (using a variadic function) and will
remove it later, once all the callers get updated.

The body of the function is reworked accordingly and is_out is
replaced by usb_pipeout(pipe). The WARN_ON() calls become unnecessary
and get removed.

Finally, the return type is changed from __u16 to u16 because this is
not a UAPI function.
Signed-off-by: Vincent Mailhol <mailhol.vincent@wanadoo.fr>
Link: https://lore.kernel.org/r/20220317035514.6378-2-mailhol.vincent@wanadoo.frSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

include/linux/usb.h

@@ -1969,21 +1969,17 @@ usb_pipe_endpoint(struct usb_device *dev, unsigned int pipe)
 	return eps[usb_pipeendpoint(pipe)];
 }
 
-/*-------------------------------------------------------------------------*/
-
-static inline __u16
-usb_maxpacket(struct usb_device *udev, int pipe, int is_out)
+static inline u16 usb_maxpacket(struct usb_device *udev, int pipe,
+				/* int is_out deprecated */ ...)
 {
 	struct usb_host_endpoint	*ep;
 	unsigned			epnum = usb_pipeendpoint(pipe);
 
-	if (is_out) {
-		WARN_ON(usb_pipein(pipe));
+	if (usb_pipeout(pipe))
 		ep = udev->ep_out[epnum];
-	} else {
-		WARN_ON(usb_pipeout(pipe));
+	else
 		ep = udev->ep_in[epnum];
-	}
+
 	if (!ep)
 		return 0;
 
@@ -1991,8 +1987,6 @@ usb_maxpacket(struct usb_device *udev, int pipe, int is_out)
 	return usb_endpoint_maxp(&ep->desc);
 }
 
-/* ----------------------------------------------------------------------- */
-
 /* translate USB error codes to codes user space understands */
 static inline int usb_translate_errors(int error_code)
 {