Input: ims-pcu - fix potential infinite loop in CDC union descriptor parsing

Input: ims-pcu - fix potential infinite loop in CDC union descriptor parsing

The driver parses CDC union descriptors in ims_pcu_get_cdc_union_desc()
by iterating through the extra descriptor data. However, it does not
verify that the bLength of each descriptor is at least 2. A malicious
device could provide a descriptor with bLength = 0, leading to an
infinite loop in the driver.

Add a check to ensure bLength is at least 2 before proceeding with
parsing.

Fixes: 628329d52474 (Input: add IMS Passenger Control Unit driver)
Cc: stable@vger.kernel.org
Assisted-by: Gemini:gemini-3.1-pro
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>