coding style: add missing space when split strings

Long strings are split across few lines; usually split occurs at
the white space between two words.
Check that the space between the two words is still present.
While there, adjust the amount of space between words.

Issue identified by checkpatch script from Linux kernel v5.1 using
the command

	find src/ -type f -exec ./tools/scripts/checkpatch.pl \
	-q --types MISSING_SPACE -f {} \;

Change-Id: I28b9a65564195ba967051add53d1c848c7b8fb30
Signed-off-by: Antonio Borneo <borneo.antonio@gmail.com>
Reviewed-on: http://openocd.zylin.com/5620
Reviewed-by: Andreas Fritiofson <andreas.fritiofson@gmail.com>
Tested-by: jenkins

src/target/nds32_cmd.c

@@ -1007,7 +1007,7 @@ static const struct command_registration nds32_exec_command_handlers[] = {
 		.handler = handle_nds32_global_stop_command,
 		.mode = COMMAND_ANY,
 		.usage = "['on'|'off']",
-		.help = "turn on/off global stop. After turning on, every load/store"
+		.help = "turn on/off global stop. After turning on, every load/store "
 			 "instructions will be stopped to check memory access.",
 	},
 	{