Use the correct identifier for media span container.

[SergioEstevao]

Fixes: #852

How to test:

• On the WPViewController class on the demo app, uncomment the lines 437 to 441.
• Start the demo app
• Tap on the media add icon
• Wait for the media to fail
• Check if error overlay on the image with icon and message shows up correctly.

Test on the iPad also.

Need Review: @diegoreymendez

[diegoreymendez]

Works nicely for me. :shipit: