drm/v3d: Handle errors from IRQ setup.

Noted in review by Dave Emett for V3D 4.2 support.

Signed-off-by: Eric Anholt <eric@anholt.net>
Link: https://patchwork.freedesktop.org/patch/msgid/20190308174336.7866-1-eric@anholt.net


Reviewed-by: Dave Emett <david.emett@broadcom.com>