ion_import_dma_buf() can return a NULL without an error code. Detect this condition & return a -EINVAL as error. Change-Id: I18d058fd374a8d00c00bb943f496f446c9f1c90d Signed-off-by: Ranjhith Kalisamy <ranjhith@codeaurora.org> Signed-off-by: Rajeev Kulkarni <krajeev@codeaurora.org>