clkdev: get rid of redundant clk_add_alias() prototype in linux/clk.h

clk_add_alias() is provided by clkdev, and is not part of the clk API.
Howver, it is prototyped in two locations: linux/clkdev.h and
linux/clk.h.  This is a mess.  Get rid of the redundant and unnecessary
version in linux/clk.h.

Acked-by: Tony Lindgren <tony@atomide.com>
Tested-by: Robert Jarzmik <robert.jarzmik@free.fr>
Acked-by: Sekhar Nori <nsekhar@ti.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>