Update doc/primitives/lrn.md

Co-authored-by: Ranu Kundu <ranu.kundu@intel.com>

Author: vpirogov

doc/primitives/lrn.md

@@ -26,7 +26,7 @@ LRN across channels:
         \src(n, c, h, w),
 \f]
 
-LRN within channel:
+LRN within a single channel:
 
 \f[
     \dst(n, c, h, w) =