[ARM] 5536/1: Move clk_add_alias() to arch/arm/common/clkdev.c

This can be used for other arm platforms too as discussed
on the linux-arm-kernel list.

Also check the return value with IS_ERR and return PTR_ERR
as suggested by Russell King.

Signed-off-by: Tony Lindgren <tony@atomide.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>