target: riscv: fix double free() in parse_reg_ranges()

The buffer 'args' is allocated and freed in the caller function
parse_reg_ranges().
There is no reason to free it, only in some special case, in the
called function parse_reg_ranges_impl().
Scan build reports:
	src/target/riscv/riscv.c:4537:2: warning: Attempt to free
	released memory [unix.Malloc]

Drop the free() in the called function.

Change-Id: I2e308670c502f8e140603b4e5c16fc568088e1a8
Signed-off-by: Antonio Borneo <borneo.antonio@gmail.com>
Reviewed-on: https://review.openocd.org/c/openocd/+/9164
Reviewed-by: Evgeniy Naydanov <evgeniy.naydanov@syntacore.com>
Tested-by: jenkins
Reviewed-by: Tomas Vanek <vanekt@fbl.cz>

src/target/riscv/riscv.c

@@ -4473,7 +4473,6 @@ static int parse_reg_ranges_impl(struct list_head *ranges, char *args,
 			}
 		} else {
 			LOG_ERROR("Invalid argument '%s'.", arg);
-			free(args);
 			return ERROR_COMMAND_SYNTAX_ERROR;
 		}