x86, reboot: Drop redundant write of reboot_mode

We write reboot_mode to BIOS location 0x472 in
native_machine_emergency_restart() (reboot.c:542) already, there is no
need to then write it again in machine_real_restart().

This means nothing gets written there for MRR_APM, but the APM call is
a poweroff call and doesn't use this memory location.

Link: http://lkml.kernel.org/n/tip-3i0pfh44c1e3jv5lab0cf7sc@git.kernel.orgSigned-off-by: H. Peter Anvin <hpa@zytor.com>

arch/x86/kernel/reboot.c

@@ -179,14 +179,6 @@ void __noreturn machine_real_restart(unsigned int type)
 	write_cr3(real_mode_header->trampoline_pgd);
 #endif
 
-	/*
-	 * Write 0x1234 to absolute memory location 0x472.  The BIOS reads
-	 * this on booting to tell it to "Bypass memory test (also warm
-	 * boot)".  This seems like a fairly standard thing that gets set by
-	 * REBOOT.COM programs, and the previous reset routine did this
-	 * too. */
-	*((unsigned short *)0x472) = reboot_mode;
-
 	/* Jump to the identity-mapped low memory code */
 #ifdef CONFIG_X86_32
 	asm volatile("jmpl *%0" : :