mm: Export symbol ksize()

Commit 7b2cd92adc5430b0c1adeb120971852b4ea1ab08 ("crypto: api - Fix
zeroing on free") added modular user of ksize(). Export that to fix
crypto.ko compilation.

Cc: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: Kirill A. Shutemov <kirill@shutemov.name>
Signed-off-by: Pekka Enberg <penberg@cs.helsinki.fi>
diff --git a/mm/slab.c b/mm/slab.c
index ddc41f3..4d00855 100644
--- a/mm/slab.c
+++ b/mm/slab.c
@@ -4457,3 +4457,4 @@
 
 	return obj_size(virt_to_cache(objp));
 }
+EXPORT_SYMBOL(ksize);