power: fg-alg: Fix double mutex lock when capacity learning aborts

When capacity learning is aborted, mutex_lock() is called twice instead
of mutex_unlock() at the end. Fix it.

Change-Id: I9b967bffafc031968fce4fbfc484dc4b2f6a45b1
Signed-off-by: Shyam Kumar Thella <sthella@codeaurora.org>