Input: synaptics-rmi4 - block s_input when F54 queue is busy

Input: synaptics-rmi4 - block s_input when F54 queue is busy

Changing the input (diagnostic report type) mid-stream changes the
report size. Since V4L2 buffers are allocated based on the size at
stream start, changing the input while streaming could lead to a
heap buffer overflow if the new size is larger than the allocated
buffers.

Prevent this by blocking VIDIOC_S_INPUT with -EBUSY if the V4L2 queue
is busy (streaming).

Fixes: 3a762dbd5347 ("[media] Input: synaptics-rmi4 - add support for F54 diagnostics")
Cc: stable@vger.kernel.org
Assisted-by: Antigravity:gemini-3.5-flash
Reviewed-by: Hans Verkuil <hverkuil+cisco@kernel.org>
Link: https://patch.msgid.link/20260626051802.4033172-5-dmitry.torokhov@gmail.com
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>