KVM: SVM: Annotate nested_svm_map with might_sleep()

The nested_svm_map() function can sleep and must not be
called from atomic context. So annotate that function.

Signed-off-by: Joerg Roedel <joerg.roedel@amd.com>
Signed-off-by: Avi Kivity <avi@redhat.com>