cifs: account for new creduid=0x%x parameter in spnego upcall string

The commit that added the creduid=0x%x parameter failed to increase the
buffer allocation to account for it.

Reported-by: J. Bruce Fields <bfields@fieldses.org>
Signed-off-by: Jeff Layton <jlayton@redhat.com>
Signed-off-by: Steve French <sfrench@us.ibm.com>