target/riscv: gdbstub: Fix dynamic CSR XML generation

Since commit 605def6 ("target/riscv: Use the RISCVException enum for CSR operations")
the CSR predicate() function was changed to return RISCV_EXCP_NONE
instead of 0 for a valid CSR, but it forgot to update the dynamic
CSR XML generation codes in gdbstub.

Fixes: 605def6 ("target/riscv: Use the RISCVException enum for CSR operations")
Reported-by: Xuzhou Cheng <xuzhou.cheng@windriver.com>
Signed-off-by: Bin Meng <bin.meng@windriver.com>
Tested-by: Xuzhou Cheng <xuzhou.cheng@windriver.com>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Message-id: 20210615085133.389887-1-bmeng.cn@gmail.com
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>

target/riscv/gdbstub.c

@@ -170,7 +170,7 @@ static int riscv_gen_dynamic_csr_xml(CPUState *cs, int base_reg)
 
     for (i = 0; i < CSR_TABLE_SIZE; i++) {
         predicate = csr_ops[i].predicate;
-        if (predicate && !predicate(env, i)) {
+        if (predicate && (predicate(env, i) == RISCV_EXCP_NONE)) {
             if (csr_ops[i].name) {
                 g_string_append_printf(s, "<reg name=\"%s\"", csr_ops[i].name);
             } else {