ext4: use i_size_read in ext4_unaligned_aio()

commit 6e6358fc3c3c862bfe9a5bc029d3f8ce43dc9765 upstream.

We haven't taken i_mutex yet, so we need to use i_size_read().

Change-Id: Ia7d94d593999484a3d565954417e1dd15c15daad
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>