arm64: dts: ti: k3-am69-aquila-dev: Fix DP regulator enable GPIO

arm64: dts: ti: k3-am69-aquila-dev: Fix DP regulator enable GPIO

Correct the DP regulator enable GPIO to index 21.
The 3.3V DP regulator was not being enabled by the assigned GPIO, as it
is routed to GPIO index 21 and not 37, which was causing instability
with displays connected over DP or via an active DP-to-HDMI adapter.

Fixes: 39ac6623b1d8 ("arm64: dts: ti: Add Aquila AM69 Support")
Cc: stable@vger.kernel.org
Signed-off-by: Franz Schnyder <franz.schnyder@toradex.com>
Reviewed-by: Francesco Dolcini <francesco.dolcini@toradex.com>
Link: https://patch.msgid.link/20260202083604.325060-2-fra.schnyder@gmail.com
Signed-off-by: Vignesh Raghavendra <vigneshr@ti.com>