drivers: clk: sunxi: Fix memory leakage in clk-sunxi.c

Fix a possible memory leak in sun4i_osc_clk_setup().
Moved clock-frequency check to save superfluous allocation.

Signed-off-by: Victor N. Ramos Mello <victornrm@gmail.com>
Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>