clk: si5351: implement remove handler

The driver has no remove function, so it does not cleanup
resources that are not under devm management.

Found by Linux Driver Verification project (linuxtesting.org).

Signed-off-by: Alexey Khoroshilov <khoroshilov@ispras.ru>
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>