Input: rmi4 - fix num_subpackets overflow in register descriptor

Input: rmi4 - fix num_subpackets overflow in register descriptor

RMI_REG_DESC_SUBPACKET_BITS is defined as 296 (37 * BITS_PER_BYTE). This
may overflow num_subpackets in struct rmi_register_desc_item which is
defined as a u8.

Fix this by changing the type of num_subpackets to u16.

Fixes: 2b6a321da9a2 ("Input: synaptics-rmi4 - add support for Synaptics RMI4 devices")
Cc: stable@vger.kernel.org
Assisted-by: Gemini:gemini-3.1-pro
Link: https://patch.msgid.link/20260505045952.1570713-4-dmitry.torokhov@gmail.com
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>