bootm, linux: fix booting Multi-File Image with "kernel+ramdisk+fdt"

Booting a "Multi-File Image" including a linux kernel, ramdisk and
fdt, generated with

mkimage -A ppc \
    -O linux \
    -T multi \
    -C gzip \
    -a 00000000 \
    -e 00000000 \
    -n "kernel-2.6+initrd+dtb" \
    -d "vmlinux.bin.gz:ramdisk_image.gz:board.dtb" \
    multi.bin

actually fails, because ramdisk start and end addresses
didn;t get initialized. This patch fixes this issue.

Tested on the KUP4K board.
Signed-off-by: NHeiko Schocher <hs@denx.de>

common/cmd_bootm.c

@@ -291,7 +291,8 @@ static int bootm_start(cmd_tbl_t *cmdtp, int flag, int argc, char *argv[])
 		return 1;
 	}
 
-	if ((images.os.type == IH_TYPE_KERNEL) &&
+	if (((images.os.type == IH_TYPE_KERNEL) ||
+	     (images.os.type == IH_TYPE_MULTI)) &&
 	    (images.os.os == IH_OS_LINUX)) {
 		/* find ramdisk */
 		ret = boot_get_ramdisk (argc, argv, &images, IH_INITRD_ARCH,