FBSD, DFBSD (future) call afs_FakeOpen in the write path

FBSD, DFBSD (future)   call afs_FakeOpen in the write path

Call afs_FakeOpen in the write path, even though nominally
it is AFS_VM_RDWR_ENV.

Change-Id: I6d24c9631f80058e3dd0d6f284ca7792253ceaaa
Reviewed-on: http://gerrit.openafs.org/2623
Reviewed-by: Derrick Brashear <shadow@dementia.org>
Tested-by: Derrick Brashear <shadow@dementia.org>