Bug 1951597. Fix BT.709 comment in qcms. r=jrmuizel,gfx-reviewers

Table 5 in ICC.1:2010 does not seem relevant, table 65 defines parametricCurveType so that seems correct.

The formula in the comment was incorrect, it is correct in the code (I checked that the code is correct).

Differential Revision: https://phabricator.services.mozilla.com/D240301

gfx/qcms/src/iccread.rs

@@ -1277,7 +1277,7 @@ impl TryFrom<TransferCharacteristics> for curveType {
                 //
                 // Inverting gives the electro-optical transfer characteristic
                 // function (EOTF) which can be represented as ICC
-                // parametricCurveType with 4 parameters (ICC.1:2010 Table 5).
+                // parametricCurveType with 4 parameters (ICC.1:2010 Table 65).
                 // Converting between the two (Lc ↔︎ Y, V ↔︎ X):
                 //
                 // Y = (a * X + b)^g  for (X >= d)
@@ -1287,7 +1287,7 @@ impl TryFrom<TransferCharacteristics> for curveType {
                 //
                 // g = 1 / 0.45
                 // a = 1 / α
-                // b = 1 - α
+                // b = 1 - a
                 // c = 1 / 4.500
                 // d = 4.500 * β
                 //