USB: Make file operations structs in drivers/usb const.

Making structs const prevents accidental bugs and with the proper debug
options they're protected against corruption.

Signed-off-by: Luiz Fernando N. Capitulino <lcapitulino@mandriva.com.br>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

diff --git a/drivers/usb/core/devices.c b/drivers/usb/core/devices.c
index c0f3734..241d373 100644
--- a/drivers/usb/core/devices.c
+++ b/drivers/usb/core/devices.c
@@ -667,7 +667,7 @@
 	return ret;
 }
 
-struct file_operations usbfs_devices_fops = {
+const struct file_operations usbfs_devices_fops = {
 	.llseek =	usb_device_lseek,
 	.read =		usb_device_read,
 	.poll =		usb_device_poll,