crypto: stm32/crc32 - fix ext4 chksum BUG_ON()

Allow use of crc_update without prior call to crc_init.
And change (and fix) driver to use CRC device even on unaligned buffers.

Fixes: b51dbe90 ("crypto: stm32 - Support for STM32 CRC32 crypto module")

Signed-off-by: Nicolas Toromanoff <nicolas.toromanoff@st.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>