powerpc: dts: t1040rdb: fix compatible string for Rev A boards

It looks like U-Boot fails to start the kernel properly when the
compatible string of the board isn't fsl,T1040RDB, so stop overriding it
from the rev-a.dts.

Fixes: 5ebb7474 ("powerpc: dts: t1040rdb: fix ports names for Seville Ethernet switch")
Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

arch/powerpc/boot/dts/fsl/t1040rdb-rev-a.dts

@@ -10,7 +10,6 @@
 
 / {
 	model = "fsl,T1040RDB-REV-A";
-	compatible = "fsl,T1040RDB-REV-A";
 };
 
 &seville_port0 {