s390/entry: Fix setting _CIF_MCCK_GUEST with lowcore relocation

When lowcore relocation is enabled, the machine check handler doesn't
use the lowcore address when setting _CIF_MCCK_GUEST. Fix this by
adding the missing base register.

Fixes: 0001b7b ("s390/entry: Make mchk_int_handler() ready for lowcore relocation")
Reported-by: Heiko Carstens <[email protected]>
Reviewed-by: Heiko Carstens <[email protected]>
Signed-off-by: Sven Schnelle <[email protected]>
Signed-off-by: Vasily Gorbik <[email protected]>

Author: svens-s390

arch/s390/kernel/entry.S

@@ -468,7 +468,7 @@ SYM_CODE_START(mcck_int_handler)
 	clgrjl	%r9,%r14, 4f
 	larl	%r14,.Lsie_leave
 	clgrjhe	%r9,%r14, 4f
-	lg	%r10,__LC_PCPU
+	lg	%r10,__LC_PCPU(%r13)
 	oi	__PCPU_FLAGS+7(%r10), _CIF_MCCK_GUEST
 4:	BPENTER	__SF_SIE_FLAGS(%r15),_TIF_ISOLATE_BP_GUEST
 	SIEEXIT __SF_SIE_CONTROL(%r15),%r13