Input: omap4-keypad - fix runtime PM error handling

In omap4_keypad_probe, the patch fix several bugs.

  1) pm_runtime_get_sync will increment pm usage counter even it
     failed. Forgetting to pm_runtime_put_noidle will result in
     reference leak.

  2) In err_unmap, forget to disable runtime of device,
     pm_runtime_enable will increase power disable depth. Thus a
     pairing decrement is needed on the error handling path to keep
     it balanced.

  3) In err_pm_disable, it will call pm_runtime_put_sync twice not
     one time.

To fix this we factor out code reading revision and disabling touchpad, and
drop PM reference once we are done talking to the device.

Fixes: f77621cc ("Input: omap-keypad - dynamically handle register offsets")
Fixes: 5ad567ff

 ("Input: omap4-keypad - wire up runtime PM handling")
Signed-off-by: Zhang Qilong <zhangqilong3@huawei.com>
Link: https://lore.kernel.org/r/20201120133918.2559681-1-zhangqilong3@huawei.com
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>