ultrahdr: updates to jpegr impl

- clang-format the code to a common guideline
- return status of areInputArgumentsValid call as-is
- rename variables for easier understanding
- reduce control code by assigning stride(s) and chroma ptr
after input validation
- if 420 color space is bt601, do not perform copy before
compressImage

TODO: ensure compressImage function takes luma ptr, chroma ptrs,
luma stride, chroma stride as well there by avoiding all
clobbering/intermediate copying

Bug:
Test: ./ultrahdr_unit_test

Change-Id: I9cda53419e1a7e8d68ddae571ea1bdd2ba5168f4