ramips: bdcom-wap2100: Fix boot failure by adding partitions compatible property

Flash partitions were moved under partition table node, but addition of
compatible property was omitted which lead to following boot failure:

 VFS: Cannot open root device "(null)" or unknown-block(0,0): error -6
 Please append a correct "root=" boot option; here are the available partitions:
 1f00           16384 mtdblock0
  (driver?)
 Kernel panic - not syncing: VFS: Unable to mount root fs on unknown-block(0,0)

Fixes: e4d9217f (ramips: improve BDCOM WAP2100-SK support)
Signed-off-by: Petr Štetiar <ynezz@true.cz>

target/linux/ramips/dts/BDCOM-WAP2100-SK.dts

@@ -66,6 +66,7 @@
 		spi-max-frequency = <10000000>;
 
 		partitions {
+			compatible = "fixed-partitions";
 			#address-cells = <1>;
 			#size-cells = <1>;