usb: f_gsi: Fix GSI enable logic for ADPL only composition

Driver enables GSI wrapper only if OUT EP is present in
GSI interface which is not the case with DPL function.
This logic works as long as there is another GSI function
present with OUT EP (e.g. RMNET/RNDIS). However, if ADPL is
the only GSI function in composition then driver does all
the EP specific programming in USB GSI wrapper but doesn't
enable it. Since, initial doorbell is rung by software, data
transfer does start but eventually stall happens as USB GSI
wrapper doesn't ring doorbell.
Fix it by not having an EP check while enabling GSI.

Change-Id: Ia40209d5a3f3b5947b13e8909ef9f994200f7a85
Signed-off-by: Manu Gautam <mgautam@codeaurora.org>