serial: core: Fold do_uart_get_info() into caller

do_uart_get_info() has a single caller: uart_get_info().
Manually inline do_uart_get_info().

Signed-off-by: Peter Hurley <peter@hurleysoftware.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>