bus: Change a few bus drivers to use consistent IVAR ranges

A few bus drivers used 1 instead of 0 as the starting index of their
private IVARs.  Fix those drivers to start at BUS_IVARS_PRIVATE for
consistency.

Differential Revision:	https://reviews.freebsd.org/D54934

sys/dev/quicc/quicc_bus.h

@@ -30,7 +30,7 @@
 #define	_DEV_QUICC_BUS_H_
 
 enum {
-	QUICC_IVAR_CLOCK = BUS_IVARS_PRIVATE + 1,	/* The CPM clock. */
+	QUICC_IVAR_CLOCK = BUS_IVARS_PRIVATE,	/* The CPM clock. */
 	QUICC_IVAR_BRGCLK,		/* The BRG clock affected by SCCR. */
 	QUICC_IVAR_DEVTYPE
 };

sys/dev/virtio/virtio.h

@@ -54,7 +54,7 @@ struct vq_alloc_info;
  * VirtIO instance variables indices.
  */
 enum {
-	VIRTIO_IVAR_DEVTYPE = BUS_IVARS_PRIVATE + 1,
+	VIRTIO_IVAR_DEVTYPE = BUS_IVARS_PRIVATE,
 	VIRTIO_IVAR_FEATURE_DESC,
 	VIRTIO_IVAR_VENDOR,
 	VIRTIO_IVAR_DEVICE,

sys/sys/cpu.h

@@ -36,7 +36,7 @@
  */
 
 enum {
-	CPU_IVAR_PCPU = BUS_IVARS_PRIVATE + 1,
+	CPU_IVAR_PCPU = BUS_IVARS_PRIVATE,
 	CPU_IVAR_NOMINAL_MHZ,
 	CPU_IVAR_CPUID_SIZE,
 	CPU_IVAR_CPUID