target/riscv/riscv-011.c: fix access to non-existent register

`reg` is a number in register cache, as evident by the following call to
`reg_cache_set()`. `CSR_DCSR` is `GDB_REGNO_DCSR - 65`. This results in
setting cache value for another register, which does not exist, and
causes a segfault if all non-existent registers are not allocated a
value (`reg->value == NULL`).

Change-Id: Iab68a4bb55ce6d4730804e9709e40ab2af8a07c6
Signed-off-by: Evgeniy Naydanov <[email protected]>

src/target/riscv/riscv-011.c

@@ -1771,10 +1771,10 @@ static riscv_error_t handle_halt_routine(struct target *target)
 					reg = S0;
 					break;
 				case 31:
-					reg = CSR_DPC;
+					reg = GDB_REGNO_DPC;
 					break;
 				case 32:
-					reg = CSR_DCSR;
+					reg = GDB_REGNO_DCSR;
 					break;
 				default:
 					assert(0);