iommu/amd: Clear amd_iommu_snp_en if snp_rmptable_init() fails

iommu_snp_enable() checks that the IOMMU can support SNP and sets
amd_iommu_snp_en, then calls snp_rmptable_init() to map the RMP table.
If that call fails, CC_ATTR_HOST_SEV_SNP is cleared but amd_iommu_snp_en
is left set. Later IOMMU initialization uses amd_iommu_snp_en to
configure the IOMMU for SNP, on the assumption that RMP setup succeeded.

Clear amd_iommu_snp_en along with CC_ATTR_HOST_SEV_SNP.

Fixes: 409f45387c93 ("x86/sev: Fix broken SNP support with KVM module built-in")
Signed-off-by: Dheeraj Kumar Srivastava <dheerajkumar.srivastava@amd.com>
Reviewed-by: Ankit Soni <Ankit.Soni@amd.com>
Signed-off-by: Vasant Hegde <vasant.hegde@amd.com>
Signed-off-by: Joerg Roedel <joerg.roedel@amd.com>