drm/qxl: fix cursor position with non-zero hotspot

drm/qxl: fix cursor position with non-zero hotspot

The SPICE protocol considers the position of a cursor to be the location
of its active pixel on the display, so the cursor is drawn with its
top-left corner at "(x - hot_spot_x, y - hot_spot_y)" but the DRM cursor
position gives the location where the top-left corner should be drawn,
with the hotspot being a hint for drivers that need it.

This fixes the location of the window resize cursors when using Fluxbox
with the QXL DRM driver and both the QXL and modesetting X drivers.

Signed-off-by: John Keeping <john@metanate.com>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: stable@vger.kernel.org
Link: http://patchwork.freedesktop.org/patch/msgid/1447845445-2116-1-git-send-email-john@metanate.com
Signed-off-by: Jani Nikula <jani.nikula@intel.com>