HID: protect hid_device::bpf by CONFIG_HID_BPF

And not by CONFIG_BPF. BPF can be selected while HID_BPF does not have
to. It actually cannot be on some platforms due to Kconfig dependences.

This saves quite some bytes on those setups.

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>