input: raspberrypi-ts: Release firmware handle when not needed

[ Upstream commit 3b8ddff780b7d12e99ae39177f84b9003097777a ]

There is no use for the firmware interface after getting the touch
buffer address, so release it.

Signed-off-by: Nicolas Saenz Julienne <nsaenzjulienne@suse.de>
Acked-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Stable-dep-of: 5bca3688bdbc ("Input: raspberrypi-ts - fix refcount leak in rpi_ts_probe")
Signed-off-by: Sasha Levin <sashal@kernel.org>