v4l: xilinx-multi-scaler: Remove volatile

v4l: xilinx-multi-scaler: Remove volatile

As per Documentation/process/volatile-considered-harmful.rst,
using accessor functions do not require volatile as accessors
are written to prevent unwanted optimization.

And we are using ioread32 and iowrite32, so volatile is not require.

This patch removes the volatile from code and remove
the below warning also

warning: passing argument 1 of 'ioread32' discards 'const volatile'
qualifier from pointer target type [-Wdiscarded-qualifiers]
     return ioread32(addr);
                     ^~~~

Signed-off-by: Suresh Gupta <suresh.gupta@xilinx.com>
Reviewed-by: Saurabh Sengar <saurabh.singh@xilinx.com>
Signed-off-by: Michal Simek <michal.simek@xilinx.com>