serial: ns16550: Provide UART base clock speed in ->getinfo()

Some callers may need the UART base clock speed value.
Provide it in the ->getinfo() callback.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>

drivers/serial/ns16550.c

@@ -476,6 +476,8 @@ static int ns16550_serial_getinfo(struct udevice *dev,
 	info->reg_width = plat->reg_width;
 	info->reg_shift = plat->reg_shift;
 	info->reg_offset = plat->reg_offset;
+	info->clock = plat->clock;
+
 	return 0;
 }