iio: dac: fix ad9739a random config compile error

WARNING: unmet direct dependencies detected for REGMAP_SPI
  Depends on [n]: SPI [=n]
  Selected by [m]:
  - AD9739A [=m] && IIO [=m] && (SPI [=n] || COMPILE_TEST [=y])
...
ERROR: modpost: "spi_write_then_read" [drivers/base/regmap/regmap-spi.ko] undefined!
ERROR: modpost: "spi_async" [drivers/base/regmap/regmap-spi.ko] undefined!
ERROR: modpost: "spi_sync" [drivers/base/regmap/regmap-spi.ko] undefined!
ERROR: modpost: "__spi_register_driver" [drivers/iio/dac/ad9739a.ko] undefined!

Fixes: e77603d ("iio: dac: support the ad9739a RF DAC")
Reported-by: k2ci <[email protected]>
Reported-by: kernel test robot <[email protected]>
Closes: https://lore.kernel.org/oe-kbuild-all/[email protected]/
Signed-off-by: Ke Sun <[email protected]>
Reviewed-by: Nuno Sa <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Jonathan Cameron <[email protected]>

Author: Ke Sun

drivers/iio/dac/Kconfig

@@ -133,7 +133,7 @@ config AD5624R_SPI
 
 config AD9739A
 	tristate "Analog Devices AD9739A RF DAC spi driver"
-	depends on SPI || COMPILE_TEST
+	depends on SPI
 	select REGMAP_SPI
 	select IIO_BACKEND
 	help