staging:iio:cdc:ad7150: Add copyright notice given substantial changes.

It seems to me that the changes made to get this ready to move out of
staging are substantial enough to warant a copyright notice addition.

Signed-off-by: Jonathan Cameron <[e-mail]>
Reviewed-by: Alexandru Ardelean <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]

drivers/staging/iio/cdc/ad7150.c

···
  * AD7150 capacitive sensor driver supporting AD7150/1/6
  *
  * Copyright 2010-2011 Analog Devices Inc.
+ * Copyright 2021 Jonathan Cameron <[e-mail]>
  */
 
 #include <linux/bitfield.h>