arm64: dts: allwinner: pinetab: Fix the panel compatible

The commit 7fa40ca7 ("arm64: allwinner: dts: a64: add DT for Early
Adopter's PineTab") introduced an ili9881-based panel device node but
didn't conform to the binding. Fix this.

Fixes: 7fa40ca7 ("arm64: allwinner: dts: a64: add DT for Early Adopter's PineTab")
Signed-off-by: Maxime Ripard <maxime@cerno.tech>
Acked-by: Chen-Yu Tsai <wens@csie.org>
Acked-by: Jernej Skrabec <jernej.skrabec@siol.net>
Link: https://lore.kernel.org/r/20210114113538.1233933-18-maxime@cerno.tech