simplify a confusing expression in SkSLSPIRVCodeGenerator
simplify a confusing expression in SkSLSPIRVCodeGenerator

Bug: skia:
Change-Id: I3ce0c174677cf93903a5fb33287dfe1df3445837
Reviewed-on: https://skia-review.googlesource.com/18141
Reviewed-by: Greg Daniel <39df0a804564ccb6cf75f18db79653821f37c1c5@google.com>
Reviewed-by: Bruce Dawson <fe9e26f3989304bf7275ed139c57fd059c63d22d@google.com>
Commit-Queue: Ethan Nicholas <d2cfb8c2f603266f4dc3a6f09acbcc0089603b37@google.com>

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