serial_txx9: fix printk format mismatch

Since the commit 4f640efb, "%lx" is not
suitable for p->mapbase (resource_size_t) in 32-bit.  This patch fixes a
compiler warning caused by the mismatch.

Signed-off-by: Atsushi Nemoto <anemo@mba.ocn.ne.jp>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>