ANDROID: usb: gadget: f_mtp: don't use le16 for u8 field

The 'bCount' field is u8. Noticed by this warning:

drivers/usb/gadget/function/f_mtp.c:264:3: warning: large integer implicitly truncated to unsigned type [-Woverflow]

Change-Id: Ie82dfd1a8986ecd3acf143e41c46822f0d1aca4f
Signed-off-by: Brian Norris <briannorris@google.com>