ramips/rt305x: fix firmware partition size for some 4MB devices

allnet_all0256n-4m, tenda_w150m and unbranded_wr512-3gn-4m have
their firmware partition set to reg = <0x50000 0x3c8000>.

However, based on the 4MB flash, the size should be 0x3b0000.

After some research in the target's history, it looks like the
changed size has been a mistake when transferring device
partitions from Makefile to DTS in 770b28f146.

This patch changes the named three devices back to 0x3b0000.

Signed-off-by: Adrian Schmutzler <freifunk@adrianschmutzler.de>

target/linux/ramips/dts/rt3050_allnet_all0256n-4m.dts

@@ -41,7 +41,7 @@
 			partition@50000 {
 				compatible = "denx,uimage";
 				label = "firmware";
-				reg = <0x50000 0x3c8000>;
+				reg = <0x50000 0x3b0000>;
 			};
 		};
 	};

target/linux/ramips/dts/rt3050_tenda_w150m.dts

@@ -48,7 +48,7 @@
 			partition@50000 {
 				compatible = "denx,uimage";
 				label = "firmware";
-				reg = <0x50000 0x3c8000>;
+				reg = <0x50000 0x3b0000>;
 			};
 		};
 	};

target/linux/ramips/dts/rt3052_unbranded_wr512-3gn-4m.dts

@@ -38,7 +38,7 @@
 			partition@50000 {
 				compatible = "denx,uimage";
 				label = "firmware";
-				reg = <0x50000 0x3c8000>;
+				reg = <0x50000 0x3b0000>;
 			};
 		};
 	};