LU-16771 llite: statfs on regular files is OK

LU-16771 llite: statfs on regular files is OK

It shouldn't be considered a bug to statfs() a regular file.
There doesn't appear to be anything directory-specific in
ll_statfs_project() that would warrant this LASSERT(), and
it can be trivially triggered from userspace.

Fixes: 2354f2f040 ("LU-16771 llite: cache statfs data for projects")
Signed-off-by: Andreas Dilger <adilger@whamcloud.com>
Change-Id: I3cf6b123e7ff40d233b4bb247935835a582b4a8f
Reviewed-on: https://review.whamcloud.com/c/fs/lustre-release/+/59898
Reviewed-by: Timothy Day <timday@amazon.com>
Reviewed-by: Alex Zhuravlev <bzzz@whamcloud.com>
Reviewed-by: Li Dongyang <dongyangli@ddn.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>