USB: musb_gadget_ep0: fix typo in service_zero_data_request()

This function uses wrong bit mask to prevent clearing RXCSR status
bits when halting an endpoint -- which results in clearing SentStall
and RxPktRdy bits (that the code actually tries to avoid); must be
a result of cut-and-paste...

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