ANDROID: GKI: add padding to struct hid_device

struct hid_device was not being tracked as a "stable" symbol in the
past, but that looks to change with some future abi requirements.  So
add needed padding now, to ensure that we can support this over the
long-term.

This does not change the existing api at all as this symbol was not
supported yet.

Bug: 151154716
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>
Change-Id: I8c3064fb7a19006a29dabbaf25c9ed1737f62e75