#15868: use a buffer's size when creating its CB in groupnorm

[bbradelTT]

Ticket

Link to Github Issue #15868

Problem description

• Some group norm tests are failing with Debug Build with an assert about CB size
• The underlying reason is that the in0 CB was always sized to the nearest tile, even when the input was row major and therefore smaller

What's changed

• Set the CB size for in0 based on the per bank size to get the right size for row major and tile input

Checklist

• Post commit CI passes across https://github.com/tenstorrent/tt-metal/actions/runs/12360041457 and https://github.com/tenstorrent/tt-metal/actions/runs/12374697868 all sub-jobs pass at least once
• Blackhole Post commit (if applicable) https://github.com/tenstorrent/tt-metal/actions/runs/12360044285
• Model regression CI testing passes (if applicable) https://github.com/tenstorrent/tt-metal/actions/runs/12360048449
• Device performance regression CI testing passes (if applicable) https://github.com/tenstorrent/tt-metal/actions/runs/12360046481
• (For models and ops writers) Full new models tests passes
• New/Existing tests provide coverage for changes (in Debug)

[bbradelTT]

@TT-BrianLiu added you as a reviewer to see if you're ok with this change.