Drivers: hv: vmbus: Fix sysfs output format for ring buffer index

Drivers: hv: vmbus: Fix sysfs output format for ring buffer index

The sysfs attributes out_read_index and out_write_index in
vmbus_drv.c currently use %d to print outbound.current_read_index
and outbound.current_write_index.

These fields are u32 values, so printing them with %d (signed) is
not logically correct. Update the format specifier to %u to
correctly match their type.

No functional change, only fixes the sysfs output format.

Signed-off-by: Alok Tiwari <alok.a.tiwari@oracle.com>
Reviewed-by: Michael Kelley <mhklinux@outlook.com>
Signed-off-by: Wei Liu <wei.liu@kernel.org>