usb: gadget: libcomposite: move MODULE_VERSION to composite.c

MODULE_VERSION and AUTHOR looks better in composite.c than in
usbstrings.c so I move it there.
I put David Brownell as the module Author as I belive he wrote most of
it.

Acked-by: Michal Nazarewicz <mina86@mina86.com>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Felipe Balbi <balbi@ti.com>