staging: usbip: userspace: usbipd.c: fix userspace build error

When build userspace code, got the following error message:
make[2]: Entering directory `/usr/src/staging-2.6/drivers/staging/usbip/userspace/src'
  CC     usbip.o
...
  CCLD   usbip
  CC     usbipd.o
usbipd.c:30:25: fatal error: stub_driver.h: No such file or directory
compilation terminated.
make[2]: *** [usbipd.o] Error 1
make[2]: Leaving directory `/usr/src/staging-2.6/drivers/staging/usbip/userspace/src'
make[1]: *** [all-recursive] Error 1
make[1]: Leaving directory `/usr/src/staging-2.6/drivers/staging/usbip/userspace'
make: *** [all] Error 2

Due to commit 756d6726 and a16941ae, stub_driver had been changed
into host_driver, so update header filename and functions name to
fix these build errors

Signed-off-by: David Chang <dchang@novell.com>
CC: Joe Perches <joe@perches.com>
Cc: matt mooney <mfm@muteddisk.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>