staging: xillybus: Fixed sparse errors

Changes:

* xillybus.h: __iomem added to struct xilly_endpoint -> registers to suppress
  "different address spaces" errors.

* xillybus_core.c: __user added as required for the same reason.

* The two member names of struct xilly_endpoint_hardware of the form
  sync_single_for_{cpu,device} were changed to something that won't look
  like the well-known functions.

* All *.c files: Variables and functions made static as required.

Reported-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Eli Billauer <eli.billauer@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>