omx-core: remove the index for the number of components

logic of the function using the array of components checks
for NULL, so the last item on the list should stop the look
up for components

Signed-off-by: Daniel Charles <daniel.charles@intel.com>
add mjpeg support in omx_components list

since omx_components is ended with NULL, NUM_COMPONENTS is not necessary.

Signed-off-by: Daniel Charles <daniel.charles@intel.com>