fix typo in cublas_gemm_example.cu comments

[katherineding]

Since CUBLAS uses column-major order, a 1D vector initialized as {1,2,3,4} should be interpreted as the matrix
|1 3|
|2 4|.
This is confirmed by the cuda output:
|1 3| |5 7| |23 31|
|2 4| dot |6 8| = |34 46|

[mnicely]

Thanks @katherineding, I'll get this fixed updated soon.