clk: samsung: exynos5250: Simplify registration of PLL rate tables

Since the _get_rate() helper has been modified to use __clk_lookup()
internally, checking of PLL input rates can be done using it and so the
registration code can be simplified.

Signed-off-by: Tomasz Figa <t.figa@samsung.com>
Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>
Reviewed-by: Sylwester Nawrocki <s.nawrocki@samsung.com>
Signed-off-by: Mike Turquette <mturquette@linaro.org>