HSI: hsi: Fix error path cleanup on client registration

HSI client structure should be freed on error path after
calling device_registration by dropping a reference to it.

Signed-off-by: Carlos Chinea <carlos.chinea@nokia.com>
Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Acked-by: Linus Walleij <linus.walleij@linaro.org>