Avoid pretending to support CMYK color xforms in SkJpegCodec

BUG=skia:

GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=4439

Change-Id: I274930fd947585e7b2a4716c5c51aef267574ddd
Reviewed-on: https://skia-review.googlesource.com/4439
Reviewed-by: Leon Scroggins <scroggo@google.com>
Commit-Queue: Matt Sarett <msarett@google.com>
1 file changed