xf86drm: Fix error handling for drmGetDevice()

Some of the error conditions in drmGetDevice() can lead to us calling
closedir(NULL) or leaking memory.  Fix these conditions the same way we
did for drmGetDevices() in commit:

        commit 8c4a1cbd
        Author: Matt Roper <matthew.d.roper@intel.com>
        Date:   Wed Sep 30 09:30:51 2015 -0700

            xf86drm: Fix error handling for drmGetDevices()

Signed-off-by: Matt Roper <matthew.d.roper@intel.com>
Reviewed-by: Emil Velikov <emil.l.velikov@gmail.com>