serial: amba-pl011: Use container_of() to get uart_amba_port

Universally adopt container_of() for all pointer conversion from
uart_port to uart_amba_port.

Signed-off-by: Daniel Thompson <daniel.thompson@linaro.org>
Cc: Peter Hurley <peter@hurleysoftware.com>
Cc: Russell King <linux@arm.linux.org.uk>
Cc: Jiri Slaby <jslaby@suse.cz>
Cc: linux-serial@vger.kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>