ARM: dts: omap3 clocks: simplify ssi aliases

update aliases for the ssi clocks ssi_ssr_fck, ssi_sst_fck and ssi_ick
to make them consistent for omap34xx and omap36xx. This makes it
possible to reference the clocks from generic omap3 dts files.

Signed-off-by: Sebastian Reichel <sre@debian.org>
Acked-by: Tero Kristo <t-kristo@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>