crypto: michael_mic - fix broken misalignment handling

The Michael MIC driver uses the cra_alignmask to ensure that pointers
presented to its update and finup/final methods are 32-bit aligned.
However, due to the way the shash API works, this is no guarantee that
the 32-bit reads occurring in the update method are also aligned, as the
size of the buffer presented to update may be of uneven length. For
instance, an update() of 3 bytes followed by a misaligned update() of 4
or more bytes will result in a misaligned access using an accessor that
is not suitable for this.

On most architectures, this does not matter, and so setting the
cra_alignmask is pointless. On architectures where this does matter,
setting the cra_alignmask does not actually solve the problem.

So let's get rid of the cra_alignmask, and use unaligned accessors
instead, where appropriate.

Cc: <stable@vger.kernel.org>
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>