Input: wm97xx: Simplify resource management

Since the commit in the Fixes tag below, 'wm->input_dev' is a managed
resource that doesn't need to be explicitly unregistered or freed (see
devm_input_allocate_device() documentation)

So, remove some unless line of code to slightly simplify it.

Fixes: c72f61e7

 ("Input: wm97xx: split out touchscreen registering")
Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Acked-by: Charles Keepax <ckeepax@opensource.cirrus.com>
Link: https://lore.kernel.org/r/87dce7e80ea9b191843fa22415ca3aef5f3cc2e6.1643529968.git.christophe.jaillet@wanadoo.fr


Signed-off-by: Mark Brown <broonie@kernel.org>