QLayoutPolicy: use qCountTrailingZeroBits() in setControlType()

This is more efficient, because it maps to a single assembler
instruction on most ISAs, and also avoids a Coverity warning about the
loop not terminating and thus 1 << i overflowing, if type == {}.

The clone class, QSizePolicy, is not affected, since it already uses
qCountTrailingZeroBits().

Amends 6c322a917a.

Coverity-Id: 474336
Pick-to: 6.5
Change-Id: Idf62d045d8ac3f0cb15196dd8664ac37d92a9cc2
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
(cherry picked from commit d71379d447e87843c5a5d91857c4ff253ad4b847)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>
(cherry picked from commit 4ed56eaafcc6270855b305d08d551f6a48c9667b)

src/gui/util/qlayoutpolicy.cpp

@@ -22,15 +22,7 @@ void QLayoutPolicy::setControlType(ControlType type)
             0x00000008 maps to 3
             etc.
     */
-
-    int i = 0;
-    while (true) {
-        if (type & (0x1 << i)) {
-            bits.ctype = i;
-            return;
-        }
-        ++i;
-    }
+    bits.ctype = qCountTrailingZeroBits(quint32(type));
 }
 
 QLayoutPolicy::ControlType QLayoutPolicy::controlType() const