MAINTAINERS: Cover hw/core/uboot_image.h within Generic Loader section

Signed-off-by: Alistair Francis <alistair.francis@wdc.com>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Message-Id: <20220509091339.26016-1-alistair.francis@wdc.com>

MAINTAINERS

@@ -2198,6 +2198,7 @@ Generic Loader
 M: Alistair Francis <alistair@alistair23.me>
 S: Maintained
 F: hw/core/generic-loader.c
+F: hw/core/uboot_image.h
 F: include/hw/core/generic-loader.h
 F: docs/system/generic-loader.rst