HID: bpf: make bus_type const in struct hid_bpf_ops

The struct bus_type pointer in hid_bpf_ops just passes the pointer to
the driver core, and the driver core can handle, and expects, a constant
pointer, so also make the pointer constant in hid_bpf_ops.

Part of the process of moving all usages of struct bus_type to be
constant to move them all to read-only memory.

Cc: Jiri Kosina <jikos@kernel.org>
Cc: Benjamin Tissoires <benjamin.tissoires@redhat.com>
Cc: linux-input@vger.kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Jiri Kosina <jkosina@suse.com>