tools: iio: iio_generic_buffer: initialize channel array pointer

Uninitialized channel pointer causes segmentation fault when we
call free(channel) during cleanup() with no channels initialized.
This happens when you exit early for usage errors.  Initialize
the pointer to NULL when it is declared.

Signed-off-by: Alison Schofield <amsfield22@gmail.com>
Cc: Daniel Baluta <daniel.baluta@gmail.com>
Tested-by: Gregor Boirie <gregor.boirie@parrot.com>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>
diff --git a/tools/iio/iio_generic_buffer.c b/tools/iio/iio_generic_buffer.c
index 0e8a1f7..ae68bf0 100644
--- a/tools/iio/iio_generic_buffer.c
+++ b/tools/iio/iio_generic_buffer.c
@@ -348,7 +348,7 @@
 	int notrigger = 0;
 	char *dummy;
 
-	struct iio_channel_info *channels;
+	struct iio_channel_info *channels = NULL;
 
 	register_cleanup();