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/flash/nor/tcl.c

@@ -1276,7 +1276,7 @@ COMMAND_HANDLER(handle_flash_bank_command)
 	}
 
 	/* check the flash bank name is unique */
-	if (get_flash_bank_by_name_noprobe(bank_name) != NULL) {
+	if (get_flash_bank_by_name_noprobe(bank_name)) {
 		/* flash bank name already exists  */
 		LOG_ERROR("flash bank name '%s' already exists", bank_name);
 		return ERROR_FAIL;