qcacld-3.0: Avoid to use incorrect key length

Current parameter passed to lim_get_crypto_digest_len will be either
SHA386 or SHA256, won't return -EINVAL in any case.
For later considering, return 0 if parameter not the 2 crypto types.

Change-Id: I6cd7481a06106138df7ba18fbe9ed4eece246607
CRs-Fixed: 2751809