ANDROID: android-verity: Prevent double-freeing metadata

If extract_metadata() fails, it will free metadata in its own error
path, so it is safe to simply return the provided error value without
worrying about resource handling/releasing.

Moreover, if we simply return in extract_metadata()'s error path, we
can assume the thread of execution will only make it down into the
free_metadata: tag area sometime after extract_metadata()'s success,
in which case metadata will need to be freed without question.

Bug: 234030265
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Change-Id: I1bf42ff9ecef3eea26543526c6955d7823d45c43
(cherry picked from commit 668e043112528306813bde9213eba6171ce48223)