KVM: Documentation: rectify rst markup in kvm_run->flags

Commit c32b1b89 ("KVM: X86: Add the Document for
KVM_CAP_X86_BUS_LOCK_EXIT") added a new flag in kvm_run->flags
documentation, and caused warning in make htmldocs:

  Documentation/virt/kvm/api.rst:5004: WARNING: Unexpected indentation
  Documentation/virt/kvm/api.rst:5004: WARNING: Inline emphasis start-string without end-string

Fix this rst markup issue.
Signed-off-by: Chenyi Qiang <chenyi.qiang@intel.com>
Message-Id: <20210226075541.27179-1-chenyi.qiang@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

Documentation/virt/kvm/api.rst

@@ -4963,7 +4963,8 @@ local APIC is not used.
 	__u16 flags;
 
 More architecture-specific flags detailing state of the VCPU that may
-affect the device's behavior. Current defined flags:
+affect the device's behavior. Current defined flags::
+
   /* x86, set if the VCPU is in system management mode */
   #define KVM_RUN_X86_SMM     (1 << 0)
   /* x86, set if bus lock detected in VM */