s390/crypto: fix scatterwalk_unmap() callers in AES-GCM

The argument of scatterwalk_unmap() is supposed to be the void* that was
returned by the previous scatterwalk_map() call.
The s390 AES-GCM implementation was instead passing the pointer to the
struct scatter_walk.

This doesn't actually break anything because scatterwalk_unmap() only uses
its argument under CONFIG_HIGHMEM and ARCH_HAS_FLUSH_ON_KUNMAP.

Fixes: bf7fa038 ("s390/crypto: add s390 platform specific aes gcm support.")
Signed-off-by: Jann Horn <jannh@google.com>
Acked-by: Harald Freudenberger <freude@linux.ibm.com>
Link: https://lore.kernel.org/r/20220517143047.3054498-1-jannh@google.comSigned-off-by: Heiko Carstens <hca@linux.ibm.com>

arch/s390/crypto/aes_s390.c

@@ -701,7 +701,7 @@ static inline void _gcm_sg_unmap_and_advance(struct gcm_sg_walk *gw,
 					     unsigned int nbytes)
 {
 	gw->walk_bytes_remain -= nbytes;
-	scatterwalk_unmap(&gw->walk);
+	scatterwalk_unmap(gw->walk_ptr);
 	scatterwalk_advance(&gw->walk, nbytes);
 	scatterwalk_done(&gw->walk, 0, gw->walk_bytes_remain);
 	gw->walk_ptr = NULL;
@@ -776,7 +776,7 @@ static int gcm_out_walk_go(struct gcm_sg_walk *gw, unsigned int minbytesneeded)
 		goto out;
 	}
 
-	scatterwalk_unmap(&gw->walk);
+	scatterwalk_unmap(gw->walk_ptr);
 	gw->walk_ptr = NULL;
 
 	gw->ptr = gw->buf;