drm/exynos: drop the use of label from exynos_dsi_register_te_irq

drm/exynos: drop the use of label from exynos_dsi_register_te_irq

Dropped the use of 'out' label from exynos_dsi_register_te_irq function
because the label isn't needed. This patch returns an error in each
error case directly not going to 'out' label.

With this patch build warning[1] is also fixed, which was reported by
kernel test robot <lkp@intel.com>

[1] https://www.spinics.net/lists/dri-devel/msg323803.html

Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Inki Dae <inki.dae@samsung.com>