crypto: stm32/hash - Fix self test issue during export

Change the wait condition to check if the hash is busy.
Context can be saved as soon as hash has finishing processing
data. Remove unused lock in the device structure.

Signed-off-by: Lionel Debieve <lionel.debieve@st.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>