crypto: omap - convert reqctx buffer to fixed-size array

crypto: omap - convert reqctx buffer to fixed-size array

The flexible array member 'buffer' in 'omap_sham_reqctx' is always
allocated with BUFLEN bytes. Replace the flexible array with a
fixed-size array and remove the now-redundant 'buflen' field.

Since 'struct omap_sham_reqctx' now includes the buffer, simplify
'reqsize' and 'statesize' and use an offsetof-based memcpy() in
omap_sham_export() and omap_sham_import().

Signed-off-by: Thorsten Blum <thorsten.blum@linux.dev>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>