clk: si5351: Do not pass struct clk in platform_data

When registering clk-si5351 by platform_data, we should not pass struct clk
for the reference clocks. Drop struct clk from platform_data and rework the
driver to use devm_clk_get of named clock references.

While at it, check for at least one valid input clock and properly prepare/
enable valid reference clocks.

Signed-off-by: Sebastian Hesselbarth <sebastian.hesselbarth@gmail.com>
Reported-by: Michael Welling <mwelling@ieee.org>
Reported-by: Jean-Francois Moine <moinejf@free.fr>
Reported-by: Russell King <rmk+linux@arm.linux.org.uk>
Tested-by: Michael Welling <mwelling@ieee.org>
Tested-by: Jean-Francois Moine <moinejf@free.fr>
Signed-off-by: Michael Turquette <mturquette@linaro.org>