media: em28xx: Fix possible memory leak of em28xx struct

The em28xx struct kref isn't being decreased after an error in the
em28xx_ir_init, leading to a possible memory leak.

A kref_put and em28xx_shutdown_buttons is added to the error handler code.

Signed-off-by: Igor Matheus Andrade Torrente <igormtorrente@gmail.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>