iio: test: Fix GTS test config

The test config contained a copy-paste error. The IIO GTS helper test
was errorneously titled as "Test IIO formatting functions" in the
menuconfig.

Change the title of the tests to reflect what is tested.

Fixes: cf996f0 ("iio: test: test gain-time-scale helpers")
Signed-off-by: Matti Vaittinen <mazziesaccount@gmail.com>
Link: https://patch.msgid.link/Z0gt5R86WdeK73u2@mva-rohm
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

Author: M-Vaittinen

drivers/iio/test/Kconfig

@@ -5,7 +5,7 @@
 
 # Keep in alphabetical order
 config IIO_GTS_KUNIT_TEST
-	tristate "Test IIO formatting functions" if !KUNIT_ALL_TESTS
+	tristate "Test IIO gain-time-scale helpers" if !KUNIT_ALL_TESTS
 	depends on KUNIT
 	select IIO_GTS_HELPER
 	select TEST_KUNIT_DEVICE_HELPERS