When verifying the decoded header before decoding the object identifier

(expecting a SPNEGO pseudo-mechanism oid), the test to verify it is a
primitive encoding is compared against the asn1 class.  Primitive is not a
class.  This brings check in line with similar check for krb/ntlmssp oid.

Signed-off-by: Chris Wright <chrisw@sous-sol.org>
Cc: Steven French <sfrench@us.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Steve French <sfrench@us.ibm.com>