Fix bug in NVME_IOCTL_SUBMIT_IO

Missing 'break' in the switch statement meant that we'd fall through
to the 'return -EINVAL' case.
diff --git a/drivers/block/nvme.c b/drivers/block/nvme.c
index 9e3c724..0956e12 100644
--- a/drivers/block/nvme.c
+++ b/drivers/block/nvme.c
@@ -1054,6 +1054,7 @@
 	case nvme_cmd_compare:
 		nents = nvme_map_user_pages(dev, io.opcode & 1, io.addr,
 								length, &sg);
+		break;
 	default:
 		return -EINVAL;
 	}