file: Remove the fd parameter to fgetvp_lookup() and fgetvp_lookup_smr()

The fd is always obtained from nameidata, so just fetch it from there
instead. No functional change intended.

Reviewed by: kib
MFC after: 1 week
Differential Revision: https://reviews.freebsd.org/D43257

(cherry picked from commit 55edc40e0c7543c6ea08a28d828bcbf0c8b5dad9)