iommu/amd: Remove unsued extern declaration amd_iommu_init_hardware()

Commit 2c0ae17 ("iommu/amd: Convert iommu initialization to state machine")
left behind this.

Signed-off-by: YueHaibing <yuehaibing@huawei.com>
Reviewed-by: Suravee Suthikulpanit <suravee.suthikulpanit@amd.com>
Link: https://lore.kernel.org/r/20230802133201.17512-1-yuehaibing@huawei.com
Signed-off-by: Joerg Roedel <jroedel@suse.de>

Author: YueHaibing

include/linux/amd-iommu.h

@@ -32,7 +32,6 @@ struct task_struct;
 struct pci_dev;
 
 extern int amd_iommu_detect(void);
-extern int amd_iommu_init_hardware(void);
 
 /**
  * amd_iommu_init_device() - Init device for use with IOMMUv2 driver