doc: Put the opening '{' at the end of combined typedefs

gtk-doc is not smart enough to parse things like:

  typedef struct
  {
    ...
  } CoglFoo;

but needs the '{' at the end of the first line.

(cherry picked from commit d1187550ef547305fdeb8a22a7e39a95611a0e1d)

cogl/cogl-error.h

@@ -113,8 +113,7 @@
  * @code: A specific error code within a specified domain
  * @message: A human readable error message
  */
-typedef struct _CoglError
-{
+typedef struct _CoglError {
   uint32_t domain;
   int code;
   char *message;

cogl/cogl-object.h

@@ -83,8 +83,7 @@ cogl_object_unref (void *object);
  *
  * Since: 1.4
  */
-typedef struct
-{
+typedef struct {
   int unused;
 } CoglUserDataKey;
 
@@ -114,8 +113,7 @@ typedef void (*CoglUserDataDestroyCallback) (void *user_data);
  * Since: 1.8
  * Stability: unstable
  */
-typedef struct
-{
+typedef struct {
   const char *name;
   unsigned long instance_count;
 } CoglDebugObjectTypeInfo;