drm/tegra: fix missing unlock on error

Add the missing unlock before return from function host1x_drm_init() and
host1x_drm_exit() in the error handling case.

Signed-off-by: Wei Yongjun <yongjun_wei@trendmicro.com.cn>
Signed-off-by: Thierry Reding <thierry.reding@avionic-design.de>