target/riscv: Check the correct exception cause in vector GDB stub

After RISCVException enum is introduced, riscv_csrrw_debug() returns
RISCV_EXCP_NONE to indicate there's no error. RISC-V vector GDB stub
should check the result against RISCV_EXCP_NONE instead of value 0.
Otherwise, 'E14' packet would be incorrectly reported for vector CSRs
when using "info reg vector" GDB command.

Signed-off-by: Frank Chang <frank.chang@sifive.com>
Reviewed-by: Jim Shu <jim.shu@sifive.com>
Reviewed-by: Tommy Wu <tommy.wu@sifive.com>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Reviewed-by: LIU Zhiwei <zhiwei_liu@linux.alibaba.com>
Message-Id: <20220918083245.13028-1-frank.chang@sifive.com>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>

target/riscv/gdbstub.c

@@ -183,7 +183,7 @@ static int riscv_gdb_get_vector(CPURISCVState *env, GByteArray *buf, int n)
     target_ulong val = 0;
     int result = riscv_csrrw_debug(env, csrno, &val, 0, 0);
 
-    if (result == 0) {
+    if (result == RISCV_EXCP_NONE) {
         return gdb_get_regl(buf, val);
     }
 
@@ -210,7 +210,7 @@ static int riscv_gdb_set_vector(CPURISCVState *env, uint8_t *mem_buf, int n)
     target_ulong val = ldtul_p(mem_buf);
     int result = riscv_csrrw_debug(env, csrno, NULL, val, -1);
 
-    if (result == 0) {
+    if (result == RISCV_EXCP_NONE) {
         return sizeof(target_ulong);
     }