Change IIO_BUFFER config to Y

* It's a bool, m was never going to be very effective.

Change-Id: Id3a70b0134340d7357b4c5625439f98517476668
diff --git a/debian/defconfig b/debian/defconfig
index 57b0a96..41a0c7e 100644
--- a/debian/defconfig
+++ b/debian/defconfig
@@ -154,7 +154,7 @@
 CONFIG_NF_CONNTRACK_TIMESTAMP=m
 
 CONFIG_IIO=m
-CONFIG_IIO_BUFFER=m
+CONFIG_IIO_BUFFER=y
 
 CONFIG_GPIO_PI4IOE5V6408=m
 CONFIG_TPU_AKIRA=m