fpu/softfloat: int_to_float ensure r fully initialised

Reported by Coverity (CID1390635). We ensure this for uint_to_float
later on so we might as well mirror that.
Signed-off-by: NAlex Bennée <alex.bennee@linaro.org>
Reviewed-by: NRichard Henderson <richard.henderson@linaro.org>
Reviewed-by: NPeter Maydell <peter.maydell@linaro.org>
Signed-off-by: NPeter Maydell <peter.maydell@linaro.org>

fpu/softfloat.c

@@ -1525,7 +1525,7 @@ FLOAT_TO_UINT(64, 64)
 
 static FloatParts int_to_float(int64_t a, float_status *status)
 {
-    FloatParts r;
+    FloatParts r = {};
     if (a == 0) {
         r.cls = float_class_zero;
         r.sign = false;