sensors: change object_manager path

As per PDI, all sensor implementation shall put object manager at
`/xyz/openbmc_project/sensors`.
[1] https://github.com/openbmc/phosphor-dbus-interfaces/blob/master/yaml/xyz/openbmc_project/Sensor/Value.interface.yaml#L20

Tested: on hardware, ipmitool sdr elist is working.
```
CPU              | 36h | ok  |  0.1 |
CPU_Kernel       | 37h | ok  |  0.1 |
CPU_User         | 38h | ok  |  0.1 |
Memory_Available | 39h | ok  |  0.1 |
Storage_RW       | 3Ah | ok  |  0.1 |
```

Signed-off-by: Nan Zhou <nanzhoumails@gmail.com>
Change-Id: Ia9b21eebf37cb22cfa4bc19f2369423ea4d5c035
1 file changed