rockchip: clk: rk3399: change extract_bits to bitfield_extract

The RK3399 clk driver still has a left-over use of extract_bits, which
can be replaced by using bitfield_extract from include/bitfield.h.
This rewrites the invocation to use the shared function.

Signed-off-by: Philipp Tomsich <philipp.tomsich@theobroma-systems.com>