Fix incorrect DMA ISR handlers being used on STM32U0

[multiplemonomials]

Summary of changes

This fixes the DMA ISR handlers not being defined with the right names for STM32U0.

Impact of changes

Attempting to use DMA SPI on STM32U0 no longer causes a chip crash due to hitting a default IRQ handler

Migration actions required

Documentation

None

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Pull request type

[X] Patch update (Bug fix / Target update / Docs update / Test update / Refactor)
[] Feature update (New feature / Functionality change / New API)
[] Major update (Breaking change E.g. Return code change / API behaviour change)

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Test results

[] No Tests required for this change (E.g docs only update)
[] Covered by existing mbed-os tests (Greentea or Unittest)
[] Tests / results supplied as part of this PR

All but one DMA SPI test now passes on STM32U0 (and I don't believe the failure is related to this).

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