x86, boot: Correct max ramdisk size name

The name in struct bootparam is ->initrd_addr_max and not ramdisk_max.
Fix that.

Signed-off-by: Borislav Petkov <bp@suse.de>
Link: http://lkml.kernel.org/r/1394633584-5509-2-git-send-email-bp@alien8.de


Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>