staging: iio: isl29028: remove out of memory log message

If the call to devm_iio_device_alloc() fails, then isl29028_probe()
logs a message saying that memory cannot be allocated. The user's system
most likely has larger issues at this point. This patch removes that
error message since the error code is passed on and the message is not
necessary.

Signed-off-by: Brian Masney <masneyb@onstation.org>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>