CMake: do not expand variables beforehand

See also:
https://invent.kde.org/plasma/libplasma/-/merge_requests/267

Signed-off-by: Andreas Sturmlechner <asturm@gentoo.org>

CMakeLists.txt

@@ -165,8 +165,8 @@ set_package_properties(Breeze PROPERTIES
     TYPE OPTIONAL
     PURPOSE "For setting the default window decoration plugin"
 )
-if (${Breeze_FOUND})
+if (Breeze_FOUND)
-    if (${BREEZE_WITH_KDECORATION})
+    if (BREEZE_WITH_KDECORATION)
         set(HAVE_BREEZE_DECO true)
     else()
         set(HAVE_BREEZE_DECO FALSE)