HID: wacom: Fix OOB write in wacom_hid_set_device_mode()

HID: wacom: Fix OOB write in wacom_hid_set_device_mode()

wacom_hid_set_device_mode() currently assumes that the HID_DG_INPUTMODE
usage is always located in the first field (field[0]) of the feature report.
However, a device can specify HID_DG_INPUTMODE in a different field.

If HID_DG_INPUTMODE is in a field other than the first one and the first
field has a report_count smaller than the usage_index of HID_DG_INPUTMODE,
this leads to an out-of-bounds write to r->field[0]->value.

Fix this by storing the field index of HID_DG_INPUTMODE in 'struct
hid_data' during feature mapping.  In wacom_hid_set_device_mode(), use
this stored field index to access the correct field and add bounds
checks to ensure both the field index and the value index are within
valid ranges before writing.

Cc: stable@vger.kernel.org
Fixes: 5ae6e89f7409 ("HID: wacom: implement the finger part of the HID generic handling")
Tested-by: Ping Cheng <ping.cheng@wacom.com>
Reviewed-by: Ping Cheng <ping.cheng@wacom.com>
Signed-off-by: Lee Jones <lee@kernel.org>
Signed-off-by: Benjamin Tissoires <bentiss@kernel.org>