m68k: Fix floatx80_lognp1 (Coverity CID1390587)

return the result of packFloatx80() instead of
dropping it.
Signed-off-by: NLaurent Vivier <laurent@vivier.eu>
Reviewed-by: NPeter Maydell <peter.maydell@linaro.org>
Reviewed-by: NPhilippe Mathieu-Daudé <f4bug@amsat.org>
Message-Id: <20180430170156.1860-1-laurent@vivier.eu>

target/m68k/softfloat.c

@@ -334,7 +334,8 @@ floatx80 floatx80_lognp1(floatx80 a, float_status *status)
     if (aSign && aExp >= one_exp) {
         if (aExp == one_exp && aSig == one_sig) {
             float_raise(float_flag_divbyzero, status);
-            packFloatx80(aSign, floatx80_infinity.high, floatx80_infinity.low);
+            return packFloatx80(aSign, floatx80_infinity.high,
+                                floatx80_infinity.low);
         }
         float_raise(float_flag_invalid, status);
         return floatx80_default_nan(status);