ARM: remove duplicate include from arch/arm/mach-dove/common.c

Jesper Juhl pointed out there is a redundant include of
linux/serial_8250.h. However it turns out both are redundant.
This patch removes them both.

Reported-by: Jesper Juhl <jj@chaosbits.net>
Signed-off-by: Andrew Lunn <andrew@lunn.ch>
Reviewed-by: Jesper Juhl <jj@chaosbits.net>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>