include/asm-i386/boot.h: This is <asm/boot.h>, not <linux/boot.h>

include/asm-i386/boot.h incorrectly has the multiple include guards
as _LINUX_BOOT_H instead of _ASM_BOOT_H.  Fix.

Signed-off-by: H. Peter Anvin <hpa@zytor.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>