drm/amdgpu: unlock on error in amdgpu_ras_debugfs_table_read()

This error path needs to unlock before returning.  While we're at it,
the correct error code from copy_to_user() failure is -EFAULT, not
-EINVAL.

Fixes: c65b0805 ("drm/amdgpu: RAS EEPROM table is now in debugfs")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Reviewed-by: Luben Tuikov <luben.tuikov@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>