usb: musb: musbhsdma: increase max_len to 1MB

MUSB's DMA controller max channel length was set to 64k.
Transfer length greater than this max value is being truncated.

Signed-off-by: Anil Shetty <anil@ti.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>