sync PI value used in opencl SQRTPI to the one used in scaddins

Otherwise the sqrtpi unittest fails in opencl mode. This value is less
precise, but consistency should be more important here, not to mention
that float doesn't have that high precision anyway.

Change-Id: I8e85b7029d33932c81009e5d48e0fe2164c68dcf
Reviewed-on: https://gerrit.libreoffice.org/64228
Tested-by: Jenkins
Reviewed-by: Luboš Luňák <l.lunak@collabora.com>
(cherry picked from commit 62b0bcfd)
Reviewed-on: https://gerrit.libreoffice.org/64458

sc/source/core/opencl/op_math.cxx

@@ -2483,7 +2483,7 @@ void OpSqrtPi::GenSlidingWindowFunction(std::stringstream &ss,
         ss << ";\n";
     }
     ss << "    return (double)sqrt(arg0 *";
-    ss << " 3.1415926535897932384626433832795f);\n";
+    ss << " 3.1415926535897932);\n";
     ss << "}";
 }
 void OpCeil::GenSlidingWindowFunction(std::stringstream &ss,