ext4: elevate write count for migrate ioctl

(cherry picked from commit 2a43a878001cc5cb7c3c7be2e8dad0a1aeb939b0)

The migrate ioctl writes to the filsystem, so we need to elevate the
write count.

Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

diff --cc fs/ext4/ext4.h
Simple merge

diff --cc fs/ext4/ioctl.c
Simple merge

diff --cc fs/ext4/migrate.c
Simple merge