dmaengine: hisi_dma: Remove some useless code

When using 'pcim_enable_device()', 'pci_alloc_irq_vectors()' is
auto-magically a managed function.

It is useless (but harmless) to record an action to explicitly call
'pci_free_irq_vectors()'.

So keep things simple, comment why and how these resources are freed, axe
some useless code and save some memory.

Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Link: https://lore.kernel.org/r/4f8932e2d0d8d092bf60272511100030e013bc72.1623875508.git.christophe.jaillet@wanadoo.fr


Signed-off-by: Vinod Koul <vkoul@kernel.org>