x86/boot: Correct setup_header.start_sys name

It is called start_sys_seg elsewhere so rename it to that. It is an
obsolete field so we could just as well directly call it __u16 __pad...

No functional change.
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: http://lkml.kernel.org/r/20170221183639.16554-1-bp@alien8.deSigned-off-by: Thomas Gleixner <tglx@linutronix.de>

arch/x86/include/uapi/asm/bootparam.h

@@ -58,7 +58,7 @@ struct setup_header {
 	__u32	header;
 	__u16	version;
 	__u32	realmode_swtch;
-	__u16	start_sys;
+	__u16	start_sys_seg;
 	__u16	kernel_version;
 	__u8	type_of_loader;
 	__u8	loadflags;