Staging: vt6655: Remove CARDvSetLoopbackMode definition.

Remove function CARDvSetLoopbackMode that is never called, along with
comments related to it.

Signed-off-by: Briana Oursler <briana.oursler@gmail.com>
Reviewed-by: Stefano Brivio <sbrivio@redhat.com>
Link: https://lore.kernel.org/r/b81f06ebc0179fbceb43c085411b372ff909b134.1585802818.git.briana.oursler@gmail.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>