fs: clean up mount_setattr control flow

Simplify the control flow of mount_setattr_{prepare,commit} so they
became easiert to follow. We kept using both an integer error variable
that was passed by pointer as well as a pointer as an indicator for
whether or not we need to revert or commit the prepared changes.
Simplify this and just use the pointer. If we successfully changed
properties the revert pointer will be NULL and if we failed to change
properties it will indicate where we failed and thus need to stop
reverting.

Cc: Seth Forshee <seth.forshee@digitalocean.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: linux-fsdevel@vger.kernel.org
Signed-off-by: Christian Brauner <brauner@kernel.org>
1 file changed