clkdev: Remove clk_register_clkdevs()

Now that we've converted the only caller over to another clkdev
API, remove this one.

Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Cc: Russell King <linux@arm.linux.org.uk>
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>