pld: fix new warnings from sparse

The new committed files add some warning from the static analyser
'sparse':
- Don't assign pointer to 0, use NULL.
- switch with no cases.

Fix them.

Change-Id: I2c02d629bd80b71c8e42553be5d9388bb9b6bcd0
Signed-off-by: Antonio Borneo <borneo.antonio@gmail.com>
Reviewed-on: https://review.openocd.org/c/openocd/+/7668
Tested-by: jenkins

src/pld/pld.c

@@ -156,8 +156,6 @@ COMMAND_HANDLER(handle_pld_load_command)
 	if (retval != ERROR_OK) {
 		command_print(CMD, "failed loading file %s to pld device %u",
 			CMD_ARGV[1], dev_id);
-		switch (retval) {
-		}
 		return retval;
 	} else {
 		gettimeofday(&end, NULL);