crypto: gcm - fix assumption that assoc has one segment

crypto: gcm - fix assumption that assoc has one segment

rfc4543(gcm(*)) code for GMAC assumes that assoc scatterlist always contains
only one segment and only makes use of this first segment. However ipsec passes
assoc with three segments when using 'extended sequence number' thus in this
case rfc4543(gcm(*)) fails to function correctly. Patch fixes this issue.

Reported-by: Chaoxing Lin <[email protected]>
Tested-by: Chaoxing Lin <[email protected]>
Cc: [email protected]
Signed-off-by: Jussi Kivilinna <[email protected]>
Signed-off-by: Herbert Xu <[email protected]>