configs/releng/syslinux/archiso_pxe-linux.cfg: add missing /boot to initrd file path

Fixes https://bugs.archlinux.org/task/68803 .

configs/releng/syslinux/archiso_pxe-linux.cfg

@@ -19,7 +19,7 @@ It allows you to install Arch Linux or perform system maintenance.
 ENDTEXT
 MENU LABEL Arch Linux install medium (x86_64, NFS)
 LINUX /%INSTALL_DIR%/boot/x86_64/vmlinuz-linux
-INITRD /%INSTALL_DIR%/boot/intel-ucode.img,/%INSTALL_DIR%/amd-ucode.img,/%INSTALL_DIR%/boot/x86_64/initramfs-linux.img
+INITRD /%INSTALL_DIR%/boot/intel-ucode.img,/%INSTALL_DIR%/boot/amd-ucode.img,/%INSTALL_DIR%/boot/x86_64/initramfs-linux.img
 APPEND archisobasedir=%INSTALL_DIR% archiso_nfs_srv=${pxeserver}:/run/archiso/bootmnt checksum verify
 SYSAPPEND 3