drm/msm: fix NULL-deref on irq uninstall

drm/msm: fix NULL-deref on irq uninstall

commit cd459c005de3e2b855a8cc7768e633ce9d018e9f upstream.

In case of early initialisation errors and on platforms that do not use
the DPU controller, the deinitilisation code can be called with the kms
pointer set to NULL.

Fixes: 9dfc06222a82 ("drm/msm: Convert to Linux IRQ interfaces")
Cc: stable@vger.kernel.org	# 5.14
Cc: Thomas Zimmermann <tzimmermann@suse.de>
Signed-off-by: Johan Hovold <johan+linaro@kernel.org>
Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Patchwork: https://patchwork.freedesktop.org/patch/525104/
Link: https://lore.kernel.org/r/20230306100722.28485-5-johan+linaro@kernel.org
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>