Staging: hv: comment out blkdev variable in blkvsc_ioctl

This variable generated an unused variable warning due to other code
in the fuction being commented out.  This comments out the variable
defination so that the code compiles without warnings.

Signed-off-by: Bill Pemberton <wfp5p@virginia.edu>
Cc: Hank Janssen <hjanssen@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>