Staging: greybus: camera: cleanup multiple checks for null pointers

Fixed coding style issue regarding null comparison at multiple lines.
Issue reported by checkpatch.pl

Signed-off-by: Sumit Pundir <pundirsumit11@gmail.com>
Acked-by: Johan Hovold <johan@kernel.org>
Reviewed-by: Alex Elder <elder@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>