crypto: keembay - use 64-bit arithmetic for computing bit_len

src_size and aad_size are defined as u32, so the following expressions are
currently being evaluated using 32-bit arithmetic:

bit_len = src_size * 8;
...
bit_len = aad_size * 8;

However, bit_len is used afterwards in a context that expects a valid
64-bit value (the lower and upper 32-bit words of bit_len are extracted
and written to hw).

In order to make sure the correct bit length is generated and the 32-bit
multiplication does not wrap around, cast src_size and aad_size to u64.

Signed-off-by: Ovidiu Panait <ovidiu.panait@windriver.com>
Acked-by: Daniele Alessandrelli <daniele.alessandrelli@intel.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>