Fix SMEM index for C in CuTe examples

[joerowell]

The static check against CSmemLayout in all of the CuTe sgemm examples checks against size<0> twice.

This has only passed thus far because size<0>(CSmemLayout{}) == size<1>(CSmemLayout{});, but it isn't strictly correct (it would imply that CSmemLayout is an BLK_M x BLK_M matrix, rather than a BLK_M x BLK_N matrix).

[thakkarV]

Good catch :)

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