Baudrate calculation depends on requested baudrate and uart clock.
This patch is checking that uartclk is also passed.

The same logic is used 8250_early.c/init_port function.
Signed-off-by: Michal Simek <michal.simek@xilinx.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>