iio: dac: ad5504: fix wrong part number in kernel-doc structure name.

Probably a bit of cut and paste where someone forgot to change the
part number.
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Reviewed-by: Lars-Peter Clausen <lars@metafoo.de>
Link: https://lore.kernel.org/r/20210314164655.408461-5-jic23@kernel.org

drivers/iio/dac/ad5504.c

@@ -39,7 +39,7 @@
 #define AD5504_DAC_PWRDN_3STATE		1
 
 /**
- * struct ad5446_state - driver instance specific data
+ * struct ad5504_state - driver instance specific data
  * @spi:			spi_device
  * @reg:		supply regulator
  * @vref_mv:		actual reference voltage used