[PATCH] serial_cs device identification fix

serial_cs's vendor/device identification got broken by Yum Rayan's change
'[PATCH] serial_cs: Reduce stack usage in serial_event()' - it changed buf
type from u_short* to char*, breaking device manufacturer & card number
retrieval.  Due to this my modem stopped from being recognized as special
case.

Code will work much better if we'll rely on first_tuple's parser instead of
doing parse ourselves.  Code also looks simpler after change.

Signed-off-by: Petr Vandrovec <vandrove@vc.cvut.cz>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>