Input: ims-pcu - fix logic error in packet reset

Input: ims-pcu - fix logic error in packet reset

ims_pcu_reset_packet() incorrectly sets have_stx to true, which implies
that the start-of-packet delimiter has already been received. This
causes the protocol parser to skip waiting for the next STX byte and
potentially process garbage data.

Correctly set have_stx to false when resetting the packet state.

Fixes: 875115b82c29 ("Input: ims-pcu - fix heap-buffer-overflow in ims_pcu_process_data()")
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>