Staging: iio: some uninitialized variable bugs

There were some uninitialized variable warnings in iio.  Two of
these came from the recent changes to how the private data was
allocated in 83f0422d "staging:iio:accel:sca3000: allocate
state in iio_dev and use iio_priv to access."

drivers/staging/iio/accel/sca3000_core.c: In function 'sca3000_probe':
drivers/staging/iio/accel/sca3000_core.c:1137:9: warning: 'st' may be used uninitialized in this function
drivers/staging/iio/adc/ad7291.c: In function 'ad7291_probe':
drivers/staging/iio/adc/ad7291.c:805:15: warning: 'chip' may be used uninitialized in this function
drivers/staging/iio/dac/ad5624r_spi.c: In function 'ad5624r_probe':
drivers/staging/iio/dac/ad5624r_spi.c:228:24: warning: 'st' may be used uninitialized in this function

Signed-off-by: Dan Carpenter <error27@gmail.com>
Acked-by: Jonathan Cameron <jic23@cam.ac.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>