QIcc: fix clang's -Wimplicit-fallthrough

Clang's -Wimplicit-fallthrough is a little stricter than gcc's.

Change-Id: Idf933e19ab2d664885743e5db6c1fbb66c8b615e
Reviewed-by: Giuseppe D'Angelo <giuseppe.dangelo@kdab.com>
(cherry picked from commit 05a139d5fb5eb3d652f24ef5ebe28c232b69c6a9)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>

src/gui/painting/qicc.cpp

@@ -800,6 +800,7 @@ QByteArray toIccProfile(const QColorSpace &space)
     case QColorSpace::TransferFunction::Hlg:
         writeCicp = true;
         fixedLengthTagCount++;
+        break;
     default:
         break;
     }