radio-iris: Perform smd close operation only once.

iris_fops_release function can be called in parallel and this may result
in accessing freed memory in close_smd operation. Serialize the access to
close_smd and call it only if it is valid.

Change-Id: I9dd00625866c2f0da12ae0d35896f0683bd1453f
Signed-off-by: Rupesh Tatiya <rtatiya@codeaurora.org>