drm/hisilicon/kirin: Set .dumb_create to drm_gem_cma_dumb_create()

The kirin drivers uses drm_gem_cma_dumb_create_internal() for its
.dumb_create implementation. The function is meant for internal use
only by drivers that require additional buffer setup.

Kirin does not do an additional setup, so convert it over to
drm_gem_cma_dumb_create().

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Tested-by: John Stultz <john.stultz@linaro.org>
Reviewed-by: Emil Velikov <emil.velikov@collabora.com>
Cc: Xu YiPing <xuyiping@hisilicon.com>
Cc: Rongrong Zou <zourongrong@gmail.com>
Cc: Xinliang Liu <z.liuxinliang@hisilicon.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200605073247.4057-13-tzimmermann@suse.de