Fix comments for SkYUVColorSpace
Fix comments for SkYUVColorSpace

Document the range of video YUV values for the U and V components, which
is different from the range for the Y component.

Change-Id: I2c0101440e351013c7b3121573a591ad9860b2e2
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/293868
Reviewed-by: Brian Osman <794c0b5534edf5601d88e1d41975d0262da12894@google.com>
Commit-Queue: Brian Osman <794c0b5534edf5601d88e1d41975d0262da12894@google.com>

google/skia,aosp-mirror/platform_external_skia,aosp-mirror/platform_external_skia,google/skia,aosp-mirror/platform_external_skia,google/skia,aosp-mirror/platform_external_skia,google/skia,aosp-mirror/platform_external_skia,aosp-mirror/platform_external_skia,aosp-mirror/platform_external_skia,google/skia,google/skia,google/skia,aosp-mirror/platform_external_skia,google/skia,aosp-mirror/platform_external_skia,google/skia,google/skia,aosp-mirror/platform_external_skia