fusefs: fix a deadlock in VOP_PUTPAGES

As of r346162 fuse now invalidates the cache during writes. But it can't do
that when writing from VOP_PUTPAGES, because the write is coming _from_ the
cache. Trying to invalidate the cache in that situation causes a deadlock
in vm_object_page_remove, because the pages in question have already been
busied by the same thread.

PR: 235774
Sponsored by: The FreeBSD Foundation