drm/vmwgfx: Fix host logging / guestinfo reading error paths

The error paths were leaking opened channels.
Fix by using dedicated error paths.

Cc: <stable@vger.kernel.org>
Signed-off-by: Thomas Hellstrom <thellstrom@vmware.com>
Reviewed-by: Brian Paul <brianp@vmware.com>
Reviewed-by: Sinclair Yeh <syeh@vmware.com>