ARM: shmobile: r8a7794: Add QSPI clock to device tree

Signed-off-by: Hisashi Nakamura <hisashi.nakamura.ak@renesas.com>
[horms: omitted device node and alias; only add clock]
[horms: use clock-indicies instead of renesas,clock-indicies]
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>
Acked-by: Geert Uytterhoeven <geert+renesas@glider.be>