drm/amd: Fix the flag setting code for interrupt request

[1] Remove the irq flags setting code since pci_alloc_irq_vectors()
handles these flags.
[2] Free the msi vectors in case of error.

Signed-off-by: Ma Jun <Jun.Ma2@amd.com>
Acked-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>