staging: bcm2835-audio: fix memory leak in bcm2835_audio_open_connection()

In bcm2835_audio_open_connection(), if VCHI connection fails or
initialisation of VCHI audio instance fails vchi_instance needs to be
deallocated otherwise it will cause a memory leak.

Signed-off-by: Aishwarya Pant <aishpant@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>