target: riscv: fix memory leak in riscv_openocd_step_impl()

The array 'wps_to_enable' is never freed.
Scan build reports:
	src/target/riscv/riscv.c:4271:6: warning: Potential leak
	of memory pointed to by 'wps_to_enable' [unix.Malloc]

Add the needed free().
While there, check if the allocation is successful.

Change-Id: I00e7ade37a43a97dcc245113ad93c48784fce609
Signed-off-by: Antonio Borneo <borneo.antonio@gmail.com>
Reviewed-on: https://review.openocd.org/c/openocd/+/9163
Reviewed-by: Evgeniy Naydanov <evgeniy.naydanov@syntacore.com>
Reviewed-by: Tomas Vanek <vanekt@fbl.cz>
Tested-by: jenkins

src/target/riscv/riscv.c

@@ -4210,9 +4210,15 @@ static int riscv_openocd_step_impl(struct target *target, bool current,
 
 	RISCV_INFO(r);
 	bool *wps_to_enable = calloc(r->trigger_count, sizeof(*wps_to_enable));
+	if (!wps_to_enable) {
+		LOG_ERROR("Out of memory");
+		return ERROR_FAIL;
+	}
+
 	if (disable_watchpoints(target, wps_to_enable) != ERROR_OK) {
 		LOG_TARGET_ERROR(target, "Failed to temporarily disable "
 				"watchpoints before single-step.");
+		free(wps_to_enable);
 		return ERROR_FAIL;
 	}
 
@@ -4257,6 +4263,8 @@ _exit:
 				"after single-step.");
 	}
 
+	free(wps_to_enable);
+
 	if (breakpoint && (riscv_add_breakpoint(target, breakpoint) != ERROR_OK)) {
 		success = false;
 		LOG_TARGET_ERROR(target, "Unable to restore the disabled breakpoint.");