cs5535-mfgpt: reuse timers that have never been set up

The MFGPT hardware may be set up only once, therefore
cs5535_mfgpt_free_timer() didn't re-set the timer's "avail" bit.  However
if a timer is freed before it has actually been in use then it may be made
available again.

Signed-off-by: Jens Rottmann <JRottmann@LiPPERTEmbedded.de>
Acked-by: Andres Salomon <dilinger@queued.net>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Jordan Crouse <jordan@cosmicpenguin.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>