binman: Allow for skip_at_start when reading entries

The offset of an entry needs to be adjusted by its skip-at-start value.
This is currently missing when reading entry data. Fix it.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/tools/binman/test/191_read_image_skip.dts b/tools/binman/test/191_read_image_skip.dts
new file mode 100644
index 0000000..31df518
--- /dev/null
+++ b/tools/binman/test/191_read_image_skip.dts
@@ -0,0 +1,23 @@
+// SPDX-License-Identifier: GPL-2.0+
+
+/dts-v1/;
+
+/ {
+	#address-cells = <1>;
+	#size-cells = <1>;
+
+	binman {
+		end-at-4gb;
+		size = <0x400>;
+		section {
+			size = <0x10>;
+			u-boot {
+			};
+		};
+		fdtmap {
+		};
+		image-header {
+			location = "end";
+		};
+	};
+};