ARM: dts: armadillo800eva Correct extal1 frequency to 24 MHz

On r8a7740/armadillo, actual clock rates are ca. 4% lower than reported
by /sys/kernel/debug/clk/clk_summary. Correct the extal1 frequency from
25 MHz to 24 MHz to fix this.

This matches the Armadillo-800 EVA Product Manual, which claims the main
crystal runs at 24 MHz, and the old legacy/reference board code.

Fixes: 25aa7ba3 ("ARM: shmobile: armadillo800eva: Sync DTS")
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>