shared/tinyusb: Increase default string descr max length to 40 chars.

When defining custom USB devices, longer strings may be needed.  Eventually
the memory for string descriptors can be allocated on demand, but for now
this bigger value should be reasonable.
Signed-off-by: Damien George <damien@micropython.org>

shared/tinyusb/tusb_config.h

@@ -104,7 +104,7 @@
 #define USBD_MAX_POWER_MA (250)
 
 #ifndef MICROPY_HW_USB_DESC_STR_MAX
-#define MICROPY_HW_USB_DESC_STR_MAX (20)
+#define MICROPY_HW_USB_DESC_STR_MAX (40)
 #endif
 
 #if CFG_TUD_CDC