Doc: Fixed random QDoc warnings

- Fixed \snippet paths
- Minor language edits
- Removed unnecessary multiple page commands in a single comment
block. For example, \fn and \qmlsignal in a single comment block
is not allowed. Such instances must be documented in separate
comment blocks.

Change-Id: I65f4518499e2600c4e1807356d4116c575e48c19
Reviewed-by: Andy Nichols <andy.nichols@digia.com>
Reviewed-by: Jerome Pasion <jerome.pasion@digia.com>

src/multimediawidgets/qcameraviewfinder.cpp

@@ -59,7 +59,7 @@ QT_BEGIN_NAMESPACE
     \inmodule QtMultimediaWidgets
     \ingroup camera
 
-    \snippet doc/src/snippets/multimedia-snippets/camera.cpp Camera
+    \snippet multimedia-snippets/camera.cpp Camera
 
 */
 

src/multimediawidgets/qgraphicsvideoitem.cpp

@@ -181,7 +181,7 @@ void QGraphicsVideoItemPrivate::_q_serviceDestroyed()
     is attached to a media object by passing a pointer to the QMediaObject
     to the setMediaObject() function.
 
-    \snippet doc/src/snippets/multimedia-snippets/video.cpp Video graphics item
+    \snippet multimedia-snippets/video.cpp Video graphics item
 
     \b {Note}: Only a single display output can be attached to a media
     object at one time.

src/multimediawidgets/qvideowidget.cpp

@@ -591,7 +591,7 @@ void QVideoWidgetPrivate::_q_dimensionsChanged()
     to media object by passing a pointer to the QMediaObject in its
     constructor, and detached by destroying the QVideoWidget.
 
-    \snippet doc/src/snippets/multimedia-snippets/video.cpp Video widget
+    \snippet multimedia-snippets/video.cpp Video widget
 
     \b {Note}: Only a single display output can be attached to a media
     object at one time.

src/multimediawidgets/qvideowidgetcontrol.cpp

@@ -58,7 +58,7 @@ QT_BEGIN_NAMESPACE
     video widget implemented by the control's media service.  This widget is
     owned by the media service and so care should be taken not to delete it.
 
-    \snippet doc/src/snippets/multimedia-snippets/video.cpp Video widget control
+    \snippet multimedia-snippets/video.cpp Video widget control
 
     QVideoWidgetControl is one of number of possible video output controls.