ARM: shmobile: r8a7791: Correct SYSCIER value

Set the SYSCIER as per the values indicated in the documentation.
The value previously used appears to been copied from the r8a7779
implementation but on closer inspection is not correct for the r8a7791.

Fixes: 5f6108bb ("ARM: shmobile: r8a7791 SYSC setup code")
Reported-by: Geert Uytterhoeven <geert@linux-m68k.org>
Acked-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>