Locking hints cannot be specified against TVFs:
SELECT *
FROM dbo.someFunction() AS F
OPTION (TABLE HINT(F, NOLOCK))
Msg 8724, Level 16, State 1, Line 2
Cannot execute query. Table-valued or OPENROWSET function 'F' cannot be specified in the TABLE HINT clause.
NOLOCK, however, is not a good idea, unless you want inconsistent data.
Moreover, it won't make the query run faster. If you're experiencing long lasting locks, tune the queries in the first place.