BugLink: https://bugs.launchpad.net/bugs/1826212

[ Upstream commit cbe4a61d ]

Currently, the error path of stm_register_device() forgets to unregister
the chrdev. Fix this.
Reported-by: Alan Cox <alan.cox@intel.com>
Signed-off-by: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Reviewed-by: Laurent Fert <laurent.fert@intel.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>
Signed-off-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>