Free image buffer on read error

Free the buffer after a read error to prevent a memory leak. This was
flagged by a Coverity scan of the coreboot project, which uses
cbootimage.

Signed-off-by: Jacob Garber <jgarber1@ualberta.ca>
Signed-off-by: Stephen Warren <swarren@nvidia.com>

src/set.c

@@ -98,6 +98,7 @@ read_from_image(char	*filename,
 	if (fread(*image, 1, (size_t)(*actual_size), fp) !=
 		(size_t)(*actual_size)) {
 		result = 1;
+		free(*image);
 		goto cleanup;
 	}