Use GrComputeTightCombinedBufferSize in GrMtlGpu::uploadToTexture

A fragment of a larger CL

Change-Id: I1063186a411da280761187ebe644460afbd67430
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/232756
Reviewed-by: Jim Van Verth <jvanverth@google.com>
Commit-Queue: Robert Phillips <robertphillips@google.com>
1 file changed