ARM: shmobile: r8a7791: remove deprecated #gpio-range-cells from dtsi

Commit a1bc260b ("gpio: clean up gpio-ranges documentation")
declares the above property deprecated. That was more than 2 years ago.
Remove it, so it doesn't get copied around needlessly.

Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>