target/hexagon: fix = vs. == mishap

target/hexagon: fix = vs. == mishap

**** Changes in v2 ****
Fix yyassert's for sign and zero extends

Coverity reports a parameter that is "set but never used".  This is caused
by an assignment operator being used instead of equality.

Co-authored-by: Taylor Simpson <tsimpson@quicinc.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Taylor Simpson <tsimpson@quicinc.com>
Reviewed-by: Anton Johansson <anjo@rev.ng>
Tested-by: Anton Johansson <anjo@rev.ng>
Message-Id: <20230428204411.1400931-1-tsimpson@quicinc.com>