mediatek: fix nmbm max-reserved-blocks for Keenetic/Netcraze devices

The devicetree set mediatek,bmt-max-reserved-blocks to 64, but the
factory firmware uses 256. With the lower value NMBM fails to locate
its signature on some boards, and the device does not boot.

Restore the factory value of 256 to match stock firmware and fix
boot on affected units.

Vendor nmbm max blocks value:
https://github.com/keenetic/kernel-49/blob/master/drivers/mtd/nmbm/nmbm-mtd.c#L31

Signed-off-by: Maxim Anisimov <maxim.anisimov.ua@gmail.com>
Link: https://github.com/openwrt/openwrt/pull/24001
Signed-off-by: Jonas Jelonek <jelonek.jonas@gmail.com>

target/linux/mediatek/dts/mt7981b-keenetic-kap-630.dtsi

@@ -138,7 +138,7 @@
 
 		mediatek,nmbm;
 		mediatek,bmt-max-ratio = <1>;
-		mediatek,bmt-max-reserved-blocks = <64>;
+		mediatek,bmt-max-reserved-blocks = <256>;
 
 		partitions {
 			compatible = "fixed-partitions";

target/linux/mediatek/dts/mt7981b-keenetic-kn-3711.dts

@@ -211,7 +211,7 @@
 
 		mediatek,nmbm;
 		mediatek,bmt-max-ratio = <1>;
-		mediatek,bmt-max-reserved-blocks = <64>;
+		mediatek,bmt-max-reserved-blocks = <256>;
 
 		partitions {
 			compatible = "fixed-partitions";

target/linux/mediatek/dts/mt7981b-keenetic-kn-3811.dts

@@ -227,7 +227,7 @@
 
 		mediatek,nmbm;
 		mediatek,bmt-max-ratio = <1>;
-		mediatek,bmt-max-reserved-blocks = <64>;
+		mediatek,bmt-max-reserved-blocks = <256>;
 
 		partitions {
 			compatible = "fixed-partitions";

target/linux/mediatek/dts/mt7981b-keenetic-kn-3911.dts

@@ -174,7 +174,7 @@
 
 		mediatek,nmbm;
 		mediatek,bmt-max-ratio = <1>;
-		mediatek,bmt-max-reserved-blocks = <64>;
+		mediatek,bmt-max-reserved-blocks = <256>;
 
 		partitions {
 			compatible = "fixed-partitions";

target/linux/mediatek/dts/mt7988d-keenetic-kn-1812.dtsi

@@ -170,7 +170,7 @@
 
 		mediatek,nmbm;
 		mediatek,bmt-max-ratio = <1>;
-		mediatek,bmt-max-reserved-blocks = <64>;
+		mediatek,bmt-max-reserved-blocks = <256>;
 
 		partitions {
 			compatible = "fixed-partitions";