musa: remove nrows_x in mul_mat_q_process_tile

[yeahdongcn]

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Fix a new warning detected by our internal CI.

[JohannesGaessler]

Previously nrows_x was needed to determine the maximum extent of valid memory. I moved that one level higher and forgot to remove the argument in mul_mat_q_process_tile. So it should simply be removed since it's not used for anything (create a new commit from master to avoid a merge conflict).

[yeahdongcn]

Previously nrows_x was needed to determine the maximum extent of valid memory. I moved that one level higher and forgot to remove the argument in mul_mat_q_process_tile. So it should simply be removed since it's not used for anything (create a new commit from master to avoid a merge conflict).

Thanks for the review! I've updated the PR based on your comments.