Char: cyclades, move spin_lock to one place

Lock whole processing in isr, avoid error-prone locking/unlocking in rx/tx
esp.  On fail paths (there was a bug in the past yet).

Signed-off-by: Jiri Slaby <jirislaby@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>