USB: fix cannot work usb storage when using ohci-sm501

When I used ohci-sm501, hcd_alloc_coherent() in map_urb_for_dma() is not
called, because usb_sg_init() always sets URB_NO_TRANSFER_DMA_MAP.

dmesg (CONFIG_USB_STORAGE_DEBUG enabled):

usb-storage: Bulk Command S 0x43425355 T 0x1 L 36 F 128 Trg 0 LUN 0 CL 6
usb-storage: usb_stor_bulk_transfer_buf: xfer 31 bytes
usb-storage: Status code 0; transferred 31/31
usb-storage: -- transfer complete
usb-storage: Bulk command transfer result=0
usb-storage: usb_stor_bulk_transfer_sglist: xfer 36 bytes, 1 entries
usb-storage: Status code -75; transferred 0/36
usb-storage: -- babble
usb-storage: Bulk data transfer result 0x3
usb-storage: Attempting to get CSW...
usb-storage: usb_stor_bulk_transfer_buf: xfer 13 bytes
usb-storage: Status code 0; transferred 13/13
usb-storage: -- transfer complete
usb-storage: Bulk status result = 0
usb-storage: Bulk Status S 0x53425355 T 0x1 R 0 Stat 0x0
usb-storage: scsi cmd done, result=0x2

Signed-off-by: Yoshihiro Shimoda <shimoda.yoshihiro@renesas.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>