staging: gs_fpgaboot: drop wrapper function 'finish_driver'

Remove the function 'finish_driver' since a direct call to
platform_device_unregister() is intuitive enough to signify the original
intention of the function being removed. Coccinelle semantic patch used to
detect this:

@@
identifier wrapper, func;
type T;
@@

*T wrapper(...)
{
(
	return func(...);
|
	func(...);
)
}

Signed-off-by: Eva Rachel Retuya <eraretuya@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>