staging: iio: fix ad7606_spi regression

As pointed out by Geert Uytterhoeven, the patch was incorrect
and breaks the driver, which was fortunately pointed out by
this gcc warning:

drivers/staging/iio/adc/ad7606_spi.c: In function ‘ad7606_spi_read_block’:
drivers/staging/iio/adc/ad7606_spi.c:34: warning: ‘data’ is used uninitialized in this function

The effect of the patch is that the data is copied into
a random memory location (from the uninitialized pointer)
instead of being byteswapped in place.

This adds the initialization for the 'data' variable back
to restore the original behavior.

Cc: Ksenija Stanojevic <[e-mail]>
Fixes: 87787e5ef727 ("Staging: iio: Fix sparse endian warning")
Signed-off-by: Arnd Bergmann <[e-mail]>
Acked-by: Geert Uytterhoeven <[e-mail]>
Signed-off-by: Jonathan Cameron <[e-mail]>

drivers/staging/iio/adc/ad7606_spi.c

···
 {
 	struct spi_device *spi = to_spi_device(dev);
 	int i, ret;
-	unsigned short *data;
+	unsigned short *data = buf;
 	__be16 *bdata = buf;
 
 	ret = spi_read(spi, buf, count * 2);