drm/amdgpu: Fix PCI device refcount leak in amdgpu_atrm_get_bios()

As comment of pci_get_class() says, it returns a pci_device with its
refcount increased and decreased the refcount for the input parameter
@from if it is not NULL.

If we break the loop in amdgpu_atrm_get_bios() with 'pdev' not NULL, we
need to call pci_dev_put() to decrease the refcount. Add the missing
pci_dev_put() to avoid refcount leak.

Fixes: d38ceaf9 ("drm/amdgpu: add core driver (v4)")
Signed-off-by: Xiongfeng Wang <wangxiongfeng2@huawei.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>