clk: fixed-rate: fix of_node_get-put imbalance

When the fixed rate clock is created by devicetree,
of_clk_add_provider is called.  Add a call to
of_clk_del_provider in the remove function to balance
it out.

Signed-off-by: Alan Tull <atull@kernel.org>
Fixes: 435779fe ("clk: fixed-rate: Convert into a module platform driver")
Signed-off-by: Stephen Boyd <sboyd@kernel.org>