USB: isp1760-hcd.c: make 2 functions static

This patch makes the following needlessly global functions static:
- enqueue_an_ATL_packet()
- enqueue_an_INT_packet()

Signed-off-by: Adrian Bunk <bunk@kernel.org>
Acked-by: Sebastian Siewior <bigeasy@linutronix.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>