usb: musb: debugfs: allow forcing host mode together with speed in testmode

Based on the musb ug, force_host bit is allowed to be set along with
force_hs or force_fs bit.

It could help to implement forced host mode via testmode on Nokia N900.

Signed-off-by: Pali Rohár <pali.rohar@gmail.com>
Signed-off-by: Bin Liu <b-liu@ti.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>