staging: r8712u: Handle some false positives from kmemleak

When this driver preallocates some URBs, kmemleak is unable to find that
allocated memory when it scans. When the driver is unloaded, that memory
is reclaimed, therefore, the report is a false positive.

Signed-off-by: Larry Finger <Larry.Finger@lwfinger.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>