update video_capture

[YixingShen]

1. add tx_busy = 1 into examples/device/video_capture/src/main.c because "if (tx_busy)" is always false.
2. Correct VIDEO_CS_VS_INTERFACE_FRAME_MJPEG to VIDEO_CS_ITF_VS_FRAME_MJPEG for #define TUD_VIDEO_DESC_CS_VS_FRM_MJPEG_DISC

[kkitayam]

Thank you for fixing tx_busy. It looks good for me. But I am not familiar with stm32f1, so I cannot comment on the changing related to it.

[hathach]

can you revert the change in the f1 family.c since it break compile with other f1 that does not use UART.

[hathach]

thank you for the fix