intel-rst: Clean up ACPI add function

There is no need to initialize the error since it is going to be assigned
with the return status of at least on of the device_create_file() call.

We can return directly in case the first file creation fails.
All the labels for goto can be removed (along with the gotos) as well.
Tell the compiler that the failures are unlikely so it can create better
binaries.

Signed-off-by: Peter Ujfalusi <peter.ujfalusi@gmail.com>
Signed-off-by: Darren Hart <dvhart@linux.intel.com>