[S390] rename lowcore field

The 16 bit value at the lowcore location with offset 0x84 is the
cpu address that is associated with an external interrupt. Rename
the field from cpu_addr to ext_cpu_addr to make that clear.

Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
diff --git a/arch/s390/kernel/entry.S b/arch/s390/kernel/entry.S
index 3705700..5f437b8 100644
--- a/arch/s390/kernel/entry.S
+++ b/arch/s390/kernel/entry.S
@@ -606,7 +606,7 @@
 	stm	%r8,%r9,__PT_PSW(%r11)
 	TRACE_IRQS_OFF
 	lr	%r2,%r11		# pass pointer to pt_regs
-	l	%r3,__LC_CPU_ADDRESS	# get cpu address + interruption code
+	l	%r3,__LC_EXT_CPU_ADDR	# get cpu address + interruption code
 	l	%r4,__LC_EXT_PARAMS	# get external parameters
 	l	%r1,BASED(.Ldo_extint)
 	basr	%r14,%r1		# call do_extint