LU-14021 llite: don't touch vma after filemap_fault

LU-14021 llite: don't touch vma after filemap_fault

In case of error filemap_fault unlock mutex vma->vm_mm->mmap_sem,
so touching vma is dangerous, it could be reused or freed.
The patch uses local file variable to skip vma.

HPE-bug-id: LUS-10240
Signed-off-by: Alexander Boyko <alexander.boyko@hpe.com>
Change-Id: I72cd086645061819fab5b8595a880db64cfb9ff7
Reviewed-on: https://review.whamcloud.com/44558
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Andrew Perepechko <andrew.perepechko@hpe.com>
Reviewed-by: Patrick Farrell <pfarrell@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>