iio: test: fix missing MODULE_LICENSE for IIO_RESCALE=m

When IIO_RESCALE_KUNIT_TEST=y and IIO_RESCALE=m,
drivers/iio/afe/iio-rescale.o is built twice causing the
MODULE_LICENSE() to be lost, as shown by:

ERROR: modpost: missing MODULE_LICENSE() in drivers/iio/afe/iio-rescale.o

Rework the build configuration to have the dependency specified in the
Kconfig.

Reported-by: Randy Dunlap <[e-mail]>
Fixes: 8e74a48d17d5 ("iio: test: add basic tests for the iio-rescale driver")
Signed-off-by: Liam Beguin <[e-mail]>
Acked-by: Randy Dunlap <[e-mail]>
Tested-by: Randy Dunlap <[e-mail]>
Reviewed-by: Masahiro Yamada <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Cc: <[e-mail]>
Signed-off-by: Jonathan Cameron <[e-mail]>

drivers/iio/test/Kconfig

···
 # Keep in alphabetical order
 config IIO_RESCALE_KUNIT_TEST
 	bool "Test IIO rescale conversion functions"
-	depends on KUNIT=y && !IIO_RESCALE
+	depends on KUNIT=y && IIO_RESCALE=y
 	default KUNIT_ALL_TESTS
 	help
 	  If you want to run tests on the iio-rescale code say Y here.

drivers/iio/test/Makefile

···
 #
 
 # Keep in alphabetical order
-obj-$(CONFIG_IIO_RESCALE_KUNIT_TEST) += iio-test-rescale.o ../afe/iio-rescale.o
+obj-$(CONFIG_IIO_RESCALE_KUNIT_TEST) += iio-test-rescale.o
 obj-$(CONFIG_IIO_TEST_FORMAT) += iio-test-format.o
 CFLAGS_iio-test-format.o += $(DISABLE_STRUCTLEAK_PLUGIN)