staging: unisys: visorbus: fix include dependency

Due to include order, the visorbus_private.h file was missing a required
include header visorbus.h. If visorchipset.c or visorbus_main.c ever were
to change the order of the includes for visobus.h and visorbus_private.h,
the code would fail to compile.

Reviewed-by: Sameer Wadgaonkar <sameer.wadgaonkar@unisys.com>
Signed-off-by: David Kershner <david.kershner@unisys.com>
Reviewed-by: Tim Sell <timothy.sell@unisys.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>