docs: Fix virtiofsd.1 location

docs: Fix virtiofsd.1 location

Patch 6a7e2bbee5 docs: add virtiofsd(1) man page introduced new man
page virtiofsd.1. Unfortunately, wrong file location is used as
source for install command. This cause installation of docs fail.

Fixing wrong location so installation is successful.

Signed-off-by: Miroslav Rezanina <[email protected]>
Message-Id: <1608747495.7195569.1581513386780[email protected]>
Reviewed-by: Peter Maydell <[email protected]>
Signed-off-by: Dr. David Alan Gilbert <[email protected]>