decodetree: Fix comparison of Field

Typo comparing the sign of the field, twice, instead of also comparing
the mask of the field (which itself encodes both position and length).

Reported-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20190604154225.26992-1-richard.henderson@linaro.org
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

scripts/decodetree.py

@@ -184,7 +184,7 @@ def str_extract(self):
         return '{0}(insn, {1}, {2})'.format(extr, self.pos, self.len)
 
     def __eq__(self, other):
-        return self.sign == other.sign and self.sign == other.sign
+        return self.sign == other.sign and self.mask == other.mask
 
     def __ne__(self, other):
         return not self.__eq__(other)