fs/writeback: skip AS_NO_DATA_INTEGRITY mappings in wait_sb_inodes()

In the Linux kernel, the following vulnerability has been resolved:

fs/writeback: skip AS_NO_DATA_INTEGRITY mappings in wait_sb_inodes()

Above the while() loop in wait_sb_inodes(), we document that we must wait

for all pages under writeback for data integrity. Consequently, if a

mapping, like fuse, traditionally does not have data integrity semantics,

there is no need to wait at all; we can simply skip these inodes.

This restores fuse back to prior behavior where syncs are no-ops. This

fixes a user regression where if a system is running a faulty fuse server

that does not reply to issued write requests, this causes wait_sb_inodes()

to wait forever.