staging:iio:dummy fix kfifo_buf kconfig dependency issue if kfifo mod…

…ular and buffer enabled for built in dummy driver.

This only occurs in the unlikely event that the example driver is built
in whilst the buffer implementation is not.

Solved by switching from a depends on to a select for this particular case.

Reported-by: Fengguang Wu <fengguang.wu@intel.com>
Reported-by: Randy Dunlap <rdunlap@infradead.org>
Acked-by: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>

drivers/staging/iio/Kconfig

@@ -37,7 +37,7 @@ config IIO_SIMPLE_DUMMY_EVENTS
 
 config IIO_SIMPLE_DUMMY_BUFFER
        boolean "Buffered capture support"
-       depends on IIO_KFIFO_BUF
+       select IIO_KFIFO_BUF
        help
          Add buffered data capture to the simple dummy driver.