cifs: eliminate cifsInodeInfo->write_behind_rc (try #6)

cifs: eliminate cifsInodeInfo->write_behind_rc (try #6)

write_behind_rc is redundant and just adds complexity to the code. What
we really want to do instead is to use mapping_set_error to reset the
flags on the mapping when we find a writeback error and can't report it
to userspace yet.

For cifs_flush and cifs_fsync, we shouldn't reset the flags since errors
returned there do get reported to userspace.

Signed-off-by: Jeff Layton <[email protected]>
Reviewed-by: Suresh Jayaraman <[email protected]>
Reviewed-by: Dave Kleikamp <[email protected]>
Signed-off-by: Steve French <[email protected]>