drm/meson: pm resume add return errno branch

pm_resump api did not handle drm_mode_config_helper_resume error.
This change add handle to return drm_mode_config_helper_resume`s
error number. This code logic is aligned with api pm_suspend.
After this change, the code maybe a bit readable.

Signed-off-by: Bernard Zhao <bernard@vivo.com>
Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200428131747.2099-1-bernard@vivo.com