coding style: use ARRAY_SIZE() when possible

We have the macro ARRAY_SIZE() already available. Use it!

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

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

Change-Id: Ic7da9b710edf118eacb08f9e222f34208c580842
Signed-off-by: Antonio Borneo <borneo.antonio@gmail.com>
Reviewed-on: http://openocd.zylin.com/5198
Tested-by: jenkins
Reviewed-by: Tomas Vanek <vanekt@fbl.cz>

src/flash/nor/ambiqmicro.c

@@ -253,8 +253,7 @@ static int ambiqmicro_read_part_info(struct flash_bank *bank)
 
 	}
 
-	if (ambiqmicro_info->target_class <
-		(sizeof(ambiqmicroParts)/sizeof(ambiqmicroParts[0])))
+	if (ambiqmicro_info->target_class < ARRAY_SIZE(ambiqmicroParts))
 		ambiqmicro_info->target_name =
 			ambiqmicroParts[ambiqmicro_info->target_class].partname;
 	else