accel: ethosu: Handle possible underflow in IFM size calculations

accel: ethosu: Handle possible underflow in IFM size calculations

If the command stream has larger padding sizes than the IFM and OFM
diminsions, then the calculations will underflow to a negative value.
The result is a very large region bounds which is caught on submit, but
it's better to catch it earlier.

Current mesa ethosu driver has a signedness bug which resulted in
padding of 127 (the max) and triggers this issue.

Reviewed-and-Tested-by: Anders Roxell <anders.roxell@linaro.org>
Link: https://patch.msgid.link/20260218-ethos-fixes-v1-3-be3fa3ea9a30@kernel.org
Signed-off-by: Rob Herring (Arm) <robh@kernel.org>