ANDROID: f2fs: add back compress inode check

f2fs_force_buffered_io() originally had two checks of
f2fs_compressed_file(), when only one was needed.  The one via
f2fs_post_read_required() got removed by ANDROID commit 4f27c8b9
("ANDROID: ext4, f2fs: enable direct I/O with inline encryption").  Then
more recently, the second was removed by upstream commit 73bfe5df
("f2fs: remove redundant compress inode check"), but this wasn't fixed
up during the merge resolution.

This incorrectly left no checks remaining, so add one back.

Reported at
https://lkml.kernel.org/r/560266ca-0164-c02e-18ea-55564683d13e@huawei.com



Fixes: db50a830 ("Merge remote-tracking branch 'aosp/upstream-f2fs-stable-linux-4.14.y' into android-4.14-stable")
Change-Id: I3f6afdd221b6e44f1caa5a92d3c751a573e284df
Signed-off-by: Eric Biggers <ebiggers@google.com>