dmabuf: Fix grammar in a comment

Signed-off-by: Bryce Harrington <bryce@osg.samsung.com>
Reviewed-by: Eric Engestrom <eric.engestrom@imgtec.com>
diff --git a/libweston/linux-dmabuf.c b/libweston/linux-dmabuf.c
index 78e77a2..a91ae85 100644
--- a/libweston/linux-dmabuf.c
+++ b/libweston/linux-dmabuf.c
@@ -471,7 +471,7 @@
  * In any case, the options are to either composite garbage or nothing,
  * or disconnect the client. This is a helper function for the latter.
  *
- * The error is sent as a INVALID_OBJECT error on the client's wl_display.
+ * The error is sent as an INVALID_OBJECT error on the client's wl_display.
  *
  * \param buffer The linux_dmabuf_buffer that is unusable.
  * \param msg A custom error message attached to the protocol error.