ARM: shmobile: r8a7790: Correct SYS DMAC clock defines

This brings the implementation into line with the documentation.

This problem was introduced when SYS DMAC clock defines were added by
ac991dce

 ("ARM: shmobile: r8a7790: Add clock index macros for DT
sources") in v3.13-rc2. I do not believe this results in any problems as
these defines do not appear to be used anywhere yet.

Acked-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>