glupload: Keep track of cached EGLImage texture format
This patch fixes the following critical warning:
CRITICAL **: 11:33:32.843: Unknown GL format 0x0 provided
It would happen during the setup of a second pipeline involving the DMABuf uploader, typically with a v4l2src element. The warning was raised because the uploader had a cached EGLImage already filled but the formats were not synchronized accordingly.