v4l: xilinx-multi-scaler: Do not allow new task when device is busy

v4l: xilinx-multi-scaler: Do not allow new task when device is busy

Driver supports multiple channel so device_run( ) can be
called for multiple time.
This patch would not allow reprograming and running
of device again when driver is waiting for IP to
complete processing.

Signed-off-by: Suresh Gupta <suresh.gupta@xilinx.com>
Reviewed-by: Satish Kumar Nagireddy <satish.nagireddy.nagireddy@xilinx.com>
Signed-off-by: Michal Simek <michal.simek@xilinx.com>