musb_gadget: suppress "parasitic" TX interrupts with CPPI

Suppress "parasitic" endpoint interrupts in the DMA mode
when using CPPI DMA driver; they're caused by the MUSB gadget
driver using the DMA request mode 0 instead of the mode 1.

Signed-off-by: Sergei Shtylyov <sshtylyov@ru.mvista.com>
Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>