clkdev: Remove of_clk_get error message

of_clk_get_by_name will print an error message if it can't find the
clock from device tree. However, that doesn't indicate clk_get will
fail. It can still succeed in clk_get_sys. Remove the error message
to avoid confusion.

Driver calling clk_get should check return value and print error
messages in their code.

Change-Id: I0627fa85cbb6260c4d5b0e8f51470198c82840ee
Signed-off-by: Junjie Wu <junjiew@codeaurora.org>