usb: gadget: mv_u3d: fix sparse warnings

Fix the following sparse warnings:

drivers/usb/gadget/mv_u3d_core.c: In function ‘mv_u3d_ep_queue’:
drivers/usb/gadget/mv_u3d_core.c:812:2: warning: cast from pointer to integer of different size [-Wpointer-to-int-cast]
drivers/usb/gadget/mv_u3d_core.c:822:14: warning: cast from pointer to integer of different size [-Wpointer-to-int-cast]
drivers/usb/gadget/mv_u3d_core.c:823:4: warning: cast from pointer to integer of different size [-Wpointer-to-int-cast]
drivers/usb/gadget/mv_u3d_core.c:823:28: warning: cast from pointer to integer of different size [-Wpointer-to-int-cast]
drivers/usb/gadget/mv_u3d_core.c: In function ‘mv_u3d_ep_dequeue’:
drivers/usb/gadget/mv_u3d_core.c:905:14: warning: cast from pointer to integer of different size [-Wpointer-to-int-cast]
drivers/usb/gadget/mv_u3d_core.c: In function ‘mv_u3d_probe’:
drivers/usb/gadget/mv_u3d_core.c:1840:3: warning: cast from pointer to integer of different size [-Wpointer-to-int-cast]
drivers/usb/gadget/mv_u3d_core.c:1855:51: warning: cast from pointer to integer of different size [-Wpointer-to-int-cast]
drivers/usb/gadget/mv_u3d_core.c:1855:17: warning: cast to pointer from integer of different size [-Wint-to-pointer-cast]
drivers/usb/gadget/mv_u3d_core.c:1858:53: warning: cast from pointer to integer of different size [-Wpointer-to-int-cast]
drivers/usb/gadget/mv_u3d_core.c:1858:18: warning: cast to pointer from integer of different size [-Wint-to-pointer-cast]
drivers/usb/gadget/mv_u3d_core.c: In function ‘mv_u3d_irq_process_tr_complete’:
drivers/usb/gadget/mv_u3d_core.c:163:21: warning: ‘remaining_length’ may be used uninitialized in this function [-Wmaybe-uninitialized]
drivers/usb/gadget/mv_u3d_core.c:125:28: note: ‘remaining_length’ was declared here

Signed-off-by: Felipe Balbi <balbi@ti.com>