[PATCH] serial_cs: Reduce stack usage in serial_event()

This patch reduces the stack usage of the function serial_event() in
serial_cs from 2212 to 228.  I used a patched version of gcc 3.4.3 on i386
with -fno-unit-at-a-time disabled.

This patch is only compile tested.
Acked-by: Randy Dunlap <rddunlap@osdl.org>
Signed-off-by: Yum Rayan <yum.rayan@gmail.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>