Fix misspelling in AVX #define.

`F_from_Half` and `Half_from_F` were running the base SSE2
implementation on sub-AVX512 Intel platforms, even though F16C is
widely available. (F16C was introduced in 2009, between AVX1 and
AVX2).

Change-Id: If0e814b9885dd556dab9278a9ea1efadf69ac925
Reviewed-on: https://skia-review.googlesource.com/c/skcms/+/827837
Commit-Queue: John Stiles <johnstiles@google.com>
Reviewed-by: Michael Ludwig <michaelludwig@google.com>
Auto-Submit: John Stiles <johnstiles@google.com>
Commit-Queue: Michael Ludwig <michaelludwig@google.com>
diff --git a/src/Transform_inl.h b/src/Transform_inl.h
index 1ed96bb..5169674 100644
--- a/src/Transform_inl.h
+++ b/src/Transform_inl.h
@@ -37,7 +37,7 @@
     #define  USING_AVX
 #endif
 #if !defined(USING_AVX_F16C) && defined(USING_AVX) && defined(__F16C__)
-    #define  USING AVX_F16C
+    #define  USING_AVX_F16C
 #endif
 #if !defined(USING_AVX2)     && defined(USING_AVX) && defined(__AVX2__)
     #define  USING_AVX2