powerpc/kvm: Fall through switch case explicitly

Implicit fallthrough warning was enabled globally which broke
the build. Make it explicit with a `fall through` comment.
Signed-off-by: Santosh Sivaraj <santosh@fossix.org>
Reviewed-by: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20190729055536.25591-1-santosh@fossix.org

arch/powerpc/kvm/book3s_32_mmu.c

@@ -239,6 +239,7 @@ static int kvmppc_mmu_book3s_32_xlate_pte(struct kvm_vcpu *vcpu, gva_t eaddr,
 				case 2:
 				case 6:
 					pte->may_write = true;
+					/* fall through */
 				case 3:
 				case 5:
 				case 7: