ultrahdr: Correct hdr white nits for linear input

The hdr white nits for linear input is set to sdr white nits. This
causes huge losses during gain map compression. For linear inputs
now we are marking peak white nits to peak hlg white nits

Bug:
Test: ./ultrahdr_sample_app -p inp_p010.yuv -w 1920 -h 1080

Change-Id: I635d7d4cb7d2d3de9b2b24a59b175e05fbb3c189