Always supply a color space (sRGB for now) with F16

bench/nanobench.cpp

Index: bench/nanobench.cpp
diff --git a/bench/nanobench.cpp b/bench/nanobench.cpp
index f7dc9c60e6fee622ca81f9996d29f30dc516c8f7..042332cf1b90cc07d117a6791fcc026a4b606eea 100644
--- a/bench/nanobench.cpp
+++ b/bench/nanobench.cpp
@@ -466,7 +466,7 @@ static void create_config(const SkCommandLineConfig* config, SkTArray<Config>* c
         CPU_CONFIG(srgb, kRaster_Backend,
                    kN32_SkColorType,  kPremul_SkAlphaType, srgbColorSpace)
         CPU_CONFIG(f16,  kRaster_Backend,
-                   kRGBA_F16_SkColorType, kPremul_SkAlphaType, nullptr)
+                   kRGBA_F16_SkColorType, kPremul_SkAlphaType, srgbColorSpace)
     }
 
     #undef CPU_CONFIG