HID: hyperv: make sure input buffer is big enough

We need at least HID_MAX_BUFFER_SIZE (4096) bytes as input buffer. HID
core depends on this as it requires every input report to be at least as
big as advertised.

Signed-off-by: David Herrmann <dh.herrmann@gmail.com>
Signed-off-by: K. Y. Srinivasan <kys@microsoft.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>