drm/udl: Increase the default URB list size to 20

It seems that the current size (4) for the URB list is too small on
some devices, and it resulted in the occasional stalls.  Increase the
default URB list size to 20 for working around it.
Acked-by: Thomas Zimmermann <tzimmermann@suse.de>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Link: https://patchwork.freedesktop.org/patch/msgid/20220908095115.23396-7-tiwai@suse.de

drivers/gpu/drm/udl/udl_main.c

@@ -20,7 +20,7 @@
 #define NR_USB_REQUEST_CHANNEL 0x12
 
 #define MAX_TRANSFER (PAGE_SIZE*16 - BULK_SIZE)
-#define WRITES_IN_FLIGHT (4)
+#define WRITES_IN_FLIGHT (20)
 #define MAX_VENDOR_DESCRIPTOR_SIZE 256
 
 static int udl_parse_vendor_descriptor(struct udl_device *udl)