[ARM] pxa: allow clk aliases

We need to support more than one name+device for a struct clk for a
small number of peripherals.  We do this by re-using struct clk alias
to another struct clk - IOW, if we find that the entry we're using is
an alias, we return the aliased entry not the one we found.

Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>