ARM: shmobile: r8a7794: Correct SDHI clock base address, labels and output-names

* Correct base address of SD3 div6 clk.
* Update div6 clock node labels
  There appears to have been some inconsistency and confusion here as on
  the r8a7790 these clocks are referred to as SD(HI)1 and SD(HI)2 while on
  the r8a7791 and r8a7794 they are referred to as SD(HI)2 and SD(HI)3.

This has no run-time affect as the clock nodes are not currently used.

Fixes: 8e181633

 ("ARM: shmobile: r8a7794: Add SDHI clocks to device tree")
Reported-by: Sergei Shtylyov <sergei.shtylyov@cogentembedded.com>
Reported-by: Geert Uytterhoeven <geert@linux-m68k.org>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>
Acked-by: Geert Uytterhoeven <geert+renesas@glider.be>