Fix twogemms! test.

Author: chriselrod

test/gemm.jl

@@ -522,7 +522,7 @@
     end
 
     function twogemms!(Ab, Bb, Cb, A, B)
-        M, N = size(C); K = size(B,1)
+        M, N = size(Cb); K = size(B,1)
         @avx for m in 1:M, k in 1:K, n in 1:N
             Ab[m,k] += Cb[m,n] * B[k,n]
             Bb[k,n] += A[m,k] * Cb[m,n]