qxl: silence uninitialized variable warning

GCC doesn't complain about this but my static checker does.  We're
passing "drawable" before initializing it.  It's not actually used so
it's harmless and I just removed it.

Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: http://patchwork.freedesktop.org/patch/msgid/20160711084716.GB31411@mwanda