HID: hid-prodikeys: remove struct pk_device

First, quirks was unused in struct pk_device.

And I see no reason for this additional level of indirection. struct
pcmidi_snd is far enough for the driver. Unless I am missing something?

So drop struct pk_device and convert all the users to use struct
pcmidi_snd directly. No need for doubled kmalloc+kfrees now.

Found by https://github.com/jirislaby/clang-struct

.

Signed-off-by: Jiri Slaby (SUSE) <jirislaby@kernel.org>
Cc: Jiri Kosina <jikos@kernel.org>
Cc: Benjamin Tissoires <benjamin.tissoires@redhat.com>
Signed-off-by: Jiri Kosina <jkosina@suse.com>