cma: Drop the right mutex

The lock that was locked was cma->lock not cma_mutex. Drop
the right one when breaking out of the loop.

Change-Id: I0a1831b23613c5220795fe2a63f9db7439268c3f
Signed-off-by: Laura Abbott <lauraa@codeaurora.org>
Signed-off-by: franciscofranco <franciscofranco.1990@gmail.com>