usb: musb: Change to direct addr in context save/restore

Since not all platforms are using the same offset 0x10 in
musb_save/restore_context() eg Blackfin the offset is 0x40,
Change the indexed address to direct.

Signed-off-by: Bob Liu <lliubbo@gmail.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>