s390: fix floating point register corruption

The critical section cleanup code misses to add the offset of the
thread_struct to the task address.
Therefore, if the critical section code gets executed, it may corrupt
the task struct or restore the contents of the floating point registers
from the wrong memory location.
Fixes d0164ee2 "s390/kernel: remove save_fpu_regs() parameter and use
__LC_CURRENT instead".
Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Reviewed-by: Hendrik Brueckner <brueckner@linux.vnet.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

arch/s390/kernel/entry.S

@@ -1191,6 +1191,7 @@ cleanup_critical:
 	clg	%r9,BASED(.Lcleanup_save_fpu_fpc_end)
 	jhe	1f
 	lg	%r2,__LC_CURRENT
+	aghi	%r2,__TASK_thread
 0:	# Store floating-point controls
 	stfpc	__THREAD_FPU_fpc(%r2)
 1:	# Load register save area and check if VX is active
@@ -1252,6 +1253,7 @@ cleanup_critical:
 	clg	%r9,BASED(.Lcleanup_load_fpu_regs_vx_ctl)
 	jhe	6f
 	lg	%r4,__LC_CURRENT
+	aghi	%r4,__TASK_thread
 	lfpc	__THREAD_FPU_fpc(%r4)
 	tm	__THREAD_FPU_flags+3(%r4),FPU_USE_VX	# VX-enabled task ?
 	lg	%r4,__THREAD_FPU_regs(%r4)	# %r4 <- reg save area