fix fallthrough when deciding lowp/highp
fix fallthrough when deciding lowp/highp

This would toss the _obs mode SkRasterPipelines into highp way too often, and is just a bug.

This fixes most diffs between the jumper and obs modes.  The rest look like FMA changes, and there are no diffs when limited to SSE4.1.

Change-Id: Ib71c2a8c720b8b1e6319d1c3354ea6f4f2d9b77f
Reviewed-on: https://skia-review.googlesource.com/c/180602
Auto-Submit: Mike Klein <14574f09dfa9b4e14759b88c3426a495a0e627b0@google.com>
Reviewed-by: Herb Derby <9e12a3d2bbf73546e47cc9958f6ba8f3215b7eaf@google.com>
Commit-Queue: Herb Derby <9e12a3d2bbf73546e47cc9958f6ba8f3215b7eaf@google.com>

google/skia,rubenvb/skia,Hikari-no-Tenshi/android_external_skia,rubenvb/skia,HalCanary/skia-hc,Hikari-no-Tenshi/android_external_skia,aosp-mirror/platform_external_skia,HalCanary/skia-hc,HalCanary/skia-hc,HalCanary/skia-hc,aosp-mirror/platform_external_skia,aosp-mirror/platform_external_skia,google/skia,google/skia,rubenvb/skia,rubenvb/skia,HalCanary/skia-hc,HalCanary/skia-hc,google/skia,aosp-mirror/platform_external_skia,google/skia,Hikari-no-Tenshi/android_external_skia,Hikari-no-Tenshi/android_external_skia,google/skia,google/skia,aosp-mirror/platform_external_skia,HalCanary/skia-hc,aosp-mirror/platform_external_skia,rubenvb/skia,HalCanary/skia-hc,rubenvb/skia,Hikari-no-Tenshi/android_external_skia,Hikari-no-Tenshi/android_external_skia,aosp-mirror/platform_external_skia,google/skia,HalCanary/skia-hc,aosp-mirror/platform_external_skia,Hikari-no-Tenshi/android_external_skia,aosp-mirror/platform_external_skia,HalCanary/skia-hc,google/skia,rubenvb/skia,rubenvb/skia,rubenvb/skia,google/skia,aosp-mirror/platform_external_skia,rubenvb/skia,Hikari-no-Tenshi/android_external_skia