Not all architectures implement asm/serial.h, and the driver doesn't appear to
need it anyway.

Cc: Paul Fulghum <paulkf@microgate.com>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: Russell King <rmk@arm.linux.org.uk>
Signed-off-by: NAndrew Morton <akpm@osdl.org>
Signed-off-by: NLinus Torvalds <torvalds@osdl.org>