Input: ad714x - convert to using managed resources

Use managed resource functions devm_request_threaded_irq,
devm_inpute_allocate_device and devm_kzalloc to simplify error handling.
Also, remove use of input_unregister_device as input_register_device itself
handles it and works as resource managed function.

To be compatible with the change, various gotos are replaced with direct
returns, and unneeded labels are dropped. With these changes remove
ad714x_remove and corresponding calls of it as they are now redundant.

Signed-off-by: Vaishali Thakkar <vthakkar1994@gmail.com>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>