usb: gadget: uvc: Use macro for interrupt endpoint status size instead of using a MAGIC number

This patch adds a MACRO for the UVC video control status (interrupt) endpoint and
removes the magic number which was being used earlier.

Some UDCs have issues supporting an interrupt IN endpoint having a max packet
size less than a particular value (say 32). It is easier in that case to simply
change the MACRO value instead of changing the max packet size value at a
number of locations.

Signed-off-by: Bhupesh Sharma <bhupesh.sharma@st.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>