staging: vt6656: add error code handling to unused variable

Add error code handling to unused 'ret' variable that was never used.
Return an error code from functions called within vnt_radio_power_on.

Issue reported by coccinelle (coccicheck).

Suggested-by: Quentin Deslandes <quentin.deslandes@itdev.co.uk>
Suggested-by: Stefano Brivio <sbrivio@redhat.com>
Reviewed-by: Quentin Deslandes <quentin.deslandes@itdev.co.uk>
Signed-off-by: John B. Wyatt IV <jbwyatt4@gmail.com>
Reviewed-by: Stefano Brivio <sbrivio@redhat.com>
Link: https://lore.kernel.org/r/20200330233900.36938-1-jbwyatt4@gmail.com


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