accel/amdxdna: Return ERR_PTR on dma_alloc_noncoherent failure

accel/amdxdna: Return ERR_PTR on dma_alloc_noncoherent failure

dma_alloc_noncoherent() returns NULL on failure, but callers of
aie2_alloc_msg_buffer() check for IS_ERR(). Return ERR_PTR(-ENOMEM)
instead of NULL to match the amdxdna_iommu_alloc() path and the
caller's error checking convention.

Fixes: ece3e8980907 ("accel/amdxdna: Allow forcing IOVA-based DMA via module parameter")
Signed-off-by: Wendy Liang <wendy.liang@amd.com>
Reviewed-by: Karol Wachowski <karol.wachowski@linux.intel.com>
Reviewed-by: Mario Limonciello (AMD) <superm1@kernel.org>
Signed-off-by: Lizhi Hou <lizhi.hou@amd.com>
Link: https://patch.msgid.link/20260323173719.2311474-1-lizhi.hou@amd.com