openocd: manually remove NULL comparisons

For the remaining NULL comparisons, remove then manually.

While there, make more readable a loop, by moving the assigment
out of the loop condition.

Change-Id: I44193aaa95813156a3a79c16b80e1ad333dc1eaf
Signed-off-by: Antonio Borneo <borneo.antonio@gmail.com>
Reviewed-on: http://openocd.zylin.com/6353
Tested-by: jenkins

src/jtag/aice/aice_usb.c

@@ -2218,7 +2218,7 @@ static int aice_execute_custom_script(const char *script)
 	if (!script_fd) {
 		return ERROR_FAIL;
 	} else {
-		while (fgets(line_buffer, LINE_BUFFER_SIZE, script_fd) != NULL) {
+		while (fgets(line_buffer, LINE_BUFFER_SIZE, script_fd)) {
 			/* execute operations */
 			set_op = false;
 			op_str = strstr(line_buffer, "set");