crypto: omap-des - handle error of pm_runtime_get_sync

pm_runtime_get_sync may not always succeed depending on SoC involved.
So handle the error appropriately ensuring usage_count is accurate in
case of failure.

Signed-off-by: Nishanth Menon <nm@ti.com>
Reviewed-by: Felipe Balbi <balbi@ti.com>
Reported-by: Joachim Eastwood <manabian@gmail.com>
Tested-by: Joachim Eastwood <manabian@gmail.com>
Acked-by: Joel Fernandes <joelf@ti.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>