USB: mxc: gadget: Fix bitfield for calculating maximum packet size

The max packet length bit mask used for isochronous endpoints
should be 0x7FF instead of 0x8FF. 0x8FF will actually clear
higher-order bits in the max packet length field.

This patch applies to 2.6.34-rc6.

Signed-off-by: Dinh Nguyen <Dinh.Nguyen@freescale.com>
Cc: stable <stable@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>