afs: afs_linux_write_end only commit copied

afs: afs_linux_write_end only commit copied

In afs_linux_write_end() only commit the number of bytes actually copied
to the page.

Reviewed-on: https://gerrit.openafs.org/12409
Reviewed-by: Jeffrey Altman <jaltman@auristor.com>
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Benjamin Kaduk <kaduk@mit.edu>
(cherry picked from commit 1cd86de2912af9ad709d2d7cf8aa35d5d28fb6b3)

Change-Id: I281078577cf3d90c1e052dacad9076cffe68586f
Reviewed-on: https://gerrit.openafs.org/12413
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Benjamin Kaduk <kaduk@mit.edu>
Reviewed-by: Stephan Wiesand <stephan.wiesand@desy.de>