Two return case misses to call release_firmware() and so leak some
memory.

This patch create a fw_release label (and so a common error path)
and use it on all return case.

Detected by CoverityScan, CID#1416422 ("Resource Leak")
Signed-off-by: Corentin Labbe <clabbe.montjoie@gmail.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>