clk: socfpga: Remove check for "reg" property in socfpga_clk_init

The function socfpga_clk_init() can support clocks that do not have a divider
register, but a fixed-divider that can be read from DTS. Therefore, the "reg"
property is not a failing condition for socfpga_clk_init().

Signed-off-by: Dinh Nguyen <dinguyen@altera.com>
Signed-off-by: Mike Turquette <mturquette@linaro.org>