ANDROID: squashfs: resolve merge conflict with 4.14.68

Commit a3f94cb9 upstream changes the way
expected length is calculated for squashfs_readpage. This got merged to
stable 4.14.68.

Android adds .readpages path to make things faster, but the above commit
conflicts with it.

We try to adapt as close to upstream as possible, while not touching the
squashfs_readpages_block() mechanism.

Signed-off-by: Sumit Semwal <sumit.semwal@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>