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>

target/hexagon/idef-parser/idef-parser.y

@@ -683,15 +683,15 @@ rvalue : FAIL
              yyassert(c, &@1, $5.type == IMMEDIATE &&
                       $5.imm.type == VALUE,
                       "SXT expects immediate values\n");
-             $$ = gen_extend_op(c, &@1, &$3, $5.imm.value, &$7, SIGNED);
+             $$ = gen_extend_op(c, &@1, &$3, 64, &$7, SIGNED);
          }
        | ZXT '(' rvalue ',' IMM ',' rvalue ')'
          {
              @1.last_column = @8.last_column;
              yyassert(c, &@1, $5.type == IMMEDIATE &&
                       $5.imm.type == VALUE,
                       "ZXT expects immediate values\n");
-             $$ = gen_extend_op(c, &@1, &$3, $5.imm.value, &$7, UNSIGNED);
+             $$ = gen_extend_op(c, &@1, &$3, 64, &$7, UNSIGNED);
          }
        | '(' rvalue ')'
          {

target/hexagon/idef-parser/parser-helpers.c

@@ -1120,7 +1120,7 @@ HexValue gen_extend_op(Context *c,
                        HexValue *value,
                        HexSignedness signedness)
 {
-    unsigned bit_width = (dst_width = 64) ? 64 : 32;
+    unsigned bit_width = (dst_width == 64) ? 64 : 32;
     HexValue value_m = *value;
     HexValue src_width_m = *src_width;