Input: ims-pcu - fix DMA mapping violation in line setup

Input: ims-pcu - fix DMA mapping violation in line setup

In ims_pcu_line_setup(), the driver uses pcu->cmd_buf as a transfer
buffer for usb_control_msg(). However, pcu->cmd_buf is embedded in the
struct ims_pcu allocation, which violates DMA mapping rules regarding
cacheline alignment.

Use a heap-allocated buffer for the line coding data instead.

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