Fix tautological comparison in GrTextureDomain.cpp

-1 is not a valid value for the GrTextureDomain::Mode enum, so certain
versions of Clang warn that the comparison is a no-op:

  ../../third_party/skia/src/gpu/effects/GrTextureDomain.cpp:70:23: warning:
  comparison of constant -1 with expression of type 'GrTextureDomain::Mode' is
  always false [-Wtautological-constant-out-of-range-compare]
      SkASSERT((Mode)-1 == fMode || textureDomain.mode() == fMode);
	       ~~~~~~~~ ^  ~~~~~

Bug: chromium:793189
Change-Id: Iba49ae15622285a62ad218dbdd78b0846338b7cb
Reviewed-on: https://skia-review.googlesource.com/82962
Reviewed-by: Chris Dalton <csmartdalton@google.com>
Commit-Queue: Chris Dalton <csmartdalton@google.com>
2 files changed