net/tls: Mark the end in scatterlist table

Function zerocopy_from_iter() unmarks the 'end' in input sgtable while
adding new entries in it. The last entry in sgtable remained unmarked.
This results in KASAN error report on using apis like sg_nents(). Before
returning, the function needs to mark the 'end' in the last entry it
adds.

Signed-off-by: Vakul Garg <vakul.garg@nxp.com>
Acked-by: Dave Watson <davejwatson@fb.com>
Signed-off-by: David S. Miller <davem@davemloft.net>