arm64: mm: don't write garbage into TTBR1_EL1 register

Stable backport commit 173358a49173 ("arm64: kpti: Add ->enable callback
to remap swapper using nG mappings") of upstream commit f992b4df did
not survive the backporting process unscathed, and ends up writing garbage
into the TTBR1_EL1 register, rather than pointing it to the zero page to
disable translations. Fix that.

Cc: <stable@vger.kernel.org> #v4.14
Reported-by: Nicolas Dechesne <nicolas.dechesne@linaro.org>
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Acked-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

arch/arm64/mm/proc.S

@@ -155,7 +155,7 @@ ENDPROC(cpu_do_switch_mm)
 
 .macro	__idmap_cpu_set_reserved_ttbr1, tmp1, tmp2
 	adrp	\tmp1, empty_zero_page
-	msr	ttbr1_el1, \tmp2
+	msr	ttbr1_el1, \tmp1
 	isb
 	tlbi	vmalle1
 	dsb	nsh