USB: Remove large struct from the stack in USB storage isd200 driver

The compiler throws the following warning when compiling for a PowerPC 64
bit machine:

drivers/usb/storage/isd200.c:580: warning: the frame size of 2208 bytes is larger than 2048 bytes

There is a struct scsi_device which is placed on the stack and is
largely responsible for such wastage. The struct is just a dummy struct
filled with NULLs and set as the scsi_cmnd->device to make the
usb_stor_Bulk_transport function happy.

This patch makes the struct static, so that it is never placed onto the
stack and silences the compiler warning.

Signed-off-by: Ian Munsie <imunsie@au.ibm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>