MIPS: KVM: fix vz.c kernel-doc notation

Fix all kernel-doc warnings in mips/kvm/vz.c as reported by the
kernel test robot:

  arch/mips/kvm/vz.c:471: warning: Function parameter or member 'out_compare' not described in '_kvm_vz_save_htimer'
  arch/mips/kvm/vz.c:471: warning: Function parameter or member 'out_cause' not described in '_kvm_vz_save_htimer'
  arch/mips/kvm/vz.c:471: warning: Excess function parameter 'compare' description in '_kvm_vz_save_htimer'
  arch/mips/kvm/vz.c:471: warning: Excess function parameter 'cause' description in '_kvm_vz_save_htimer'
  arch/mips/kvm/vz.c:1551: warning: No description found for return value of 'kvm_trap_vz_handle_cop_unusable'
  arch/mips/kvm/vz.c:1552: warning: expecting prototype for kvm_trap_vz_handle_cop_unusuable(). Prototype was for kvm_trap_vz_handle_cop_unusable() instead
  arch/mips/kvm/vz.c:1597: warning: No description found for return value of 'kvm_trap_vz_handle_msa_disabled'

Fixes: c992a4f6 ("KVM: MIPS: Implement VZ support")
Fixes: f4474d50

 ("KVM: MIPS/VZ: Support hardware guest timer")
Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Reported-by: kernel test robot <lkp@intel.com>
Cc: Thomas Bogendoerfer <tsbogend@alpha.franken.de>
Cc: linux-mips@vger.kernel.org
Cc: Huacai Chen <chenhuacai@kernel.org>
Cc: Aleksandar Markovic <aleksandar.qemu.devel@gmail.com>
Cc: James Hogan <jhogan@kernel.org>
Cc: kvm@vger.kernel.org
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>