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>