USB: Gadget: Composite: Debug interface comparison

While checking valid interface number we should compare MAX_CONFIG_INTERFACES
with the variable 'intf' (which holds the lower 8bits of w_index) rather than
'w_index'

Signed-off-by: Jassi Brar <jassi.brar@samsung.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>