rs6000: Don't use operands[] for temporaries in define_expand

rs6000: Don't use operands[] for temporaries in define_expand

In ac001f5ce604 Alan fixed my thinko using operands that do not refer
to anything mentioned in the RTL pattern.  Instead, it just uses fresh
new local rtxes for those.

This patch takes that a tiny bit further: it uses local rtx for all
temporaries used in the expanders.  As a bonus that simplifies the code
a tiny bit as well.

2020-11-06  Segher Boessenkool  <segher@kernel.crashing.org>

	* config/rs6000/rs6000.md (@tablejump<mode>_normal): Don't abuse
	operands[].
	(@tablejump<mode>_nospec): Ditto.