staging: android: ion: tegra: Replace IS_ERR_OR_NULL with IS_ERR

Replace IS_ERR_OR_NULL test with an IS_ERR test since
ion_device_create() function returns a valid device or a -PTR_ERR
only as evidenced by the comment on the function prototype.

Signed-off-by: Amitoj Kaur Chawla <amitoj1606@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>