io-cache: fix unsafe typcasting of pointer to uint64

The typecast of pointer to uint64_t *, followed by setting of
64bit in inode_ctx_get() results in memory corruption on 32bit
system.

Change-Id: I32fa3bf3b853ed2690a9b9a471099a59b9d7186a
BUG: 997902
Signed-off-by: Anand Avati <avati@redhat.com>
Reviewed-on: http://review.gluster.org/5682
Tested-by: Morten Johansen <morten@bzzt.no>
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: Santosh Pradhan <spradhan@redhat.com>
Reviewed-by: Brian Foster <bfoster@redhat.com>