Input: sparse-keymap - use a managed allocation for keymap copy

Input: sparse-keymap - use a managed allocation for keymap copy

Some platform drivers use devm_input_allocate_device() together with
sparse_keymap_setup() in their .probe callbacks.  While using the former
simplifies error handling, using the latter necessitates calling
sparse_keymap_free() in the error path and upon module unloading to
avoid leaking the copy of the keymap allocated by sparse_keymap_setup().

To help prevent such leaks and enable simpler error handling, make
sparse_keymap_setup() use devm_kmemdup() to create the keymap copy so
that it gets automatically freed.

This works for both managed and non-managed input devices as the keymap
is freed after the last reference to the input device is dropped.

Note that actions previously taken by sparse_keymap_free(), i.e. taking
the input device's mutex and zeroing its keycode and keycodemax fields,
are now redundant because the managed keymap will always be freed after
the input device is unregistered.

Signed-off-by: Michał Kępień <kernel@kempniu.pl>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>