staging: android: lowmemorykiller: set TIF_MEMDIE before send kill sig

Set TIF_MEMDIE tsk_thread flag before send kill signal to the
selected thread. This is to fit a usual code sequence and avoid
potential race issue.

Signed-off-by: Weijie Yang <weijie.yang@samsung.com>
Acked-by: David Rientjes <rientjes@google.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
(cherry picked from commit 6bc2b856bb7c49f238914d965c0b1057ec78226e)

Change-Id: I3c4869d525ce80d339ec3742382beae2ee45f76e
Signed-off-by: Alex Naidis <alex.naidis@linux.com>