Update rounding/clamping comments on sk_linear_to_srgb().

tests/SRGBTest.cpp

Index: tests/SRGBTest.cpp
diff --git a/tests/SRGBTest.cpp b/tests/SRGBTest.cpp
index 95d2866fdc5e5a2d709d0603c7ed25bb37cf52e6..65bfc59b427fd07d8135ca28bc16b5459ea7201b 100644
--- a/tests/SRGBTest.cpp
+++ b/tests/SRGBTest.cpp
@@ -11,7 +11,8 @@
 #include <math.h>
 
 static uint8_t linear_to_srgb(float l) {
-    return (uint8_t)roundf(sk_linear_to_srgb(Sk4f{l})[0]);
+    // Round float to int, truncate that to uint8_t.
+    return (uint8_t)Sk4f_round( sk_linear_to_srgb(Sk4f{l}) )[0];
 }
 
 DEF_TEST(sk_linear_to_srgb, r) {