mptcp: drop unneeded type casts for hmac

Drop the unneeded type casts to 'unsigned long long' for printing out the
hmac values in add_addr_hmac_valid() and subflow_thmac_valid().

Signed-off-by: Geliang Tang <geliang.tang@suse.com>
Signed-off-by: Mat Martineau <mathew.j.martineau@linux.intel.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>