Let fallback crash dumping write to dumpstate pipes.

Fix the following denial:
    avc: denied { append } for pid=1093 comm="mediaextractor" path="pipe:[68438]" dev="pipefs" ino=68438 scontext=u:r:mediaextractor:s0 tcontext=u:r:dumpstate:s0 tclass=fifo_file permissive=1 ppid=1 pcomm="init" pgid=1 pgcomm="init"

Bug: http://b/38444258
Test: none
Change-Id: I58162e3a28b744a58396e77d6b0e2becb5633d6a
(cherry picked from commit 5efadd91)