CR-1224365 Fix xrt-smi examine alveo platform error

[rchane]

Problem solved by the commit

https://jira.xilinx.com/browse/CR-1224365 On certain alveo cards, xrt-smi examine -r platform fails

Bug / issue (if any) fixed, which PR introduced the bug, how it was discovered

Fixed ptree access issue after clocks ptree was changed previously, discovered during regression testing.

How problem was solved, alternative solutions (if any) and why they were rejected

Fixed ptree access to properly obtain clock subtree.

Risks (if any) associated the changes in the commit

N/A

What has been tested and how, request additional testing if necessary

Tested on u55.

xrt-smi examine -d e2:00 -r platform
WARNING: Unexpected xocl version (2.19.57) was found. Expected 2.19.0, to match XRT tools.

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[0000:e2:00.1] : xilinx_u55c_gen3x16_xdma_base_3
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Platform
  XSA Name               : xilinx_u55c_gen3x16_xdma_base_3 
  Logic UUID             : 97088961-FEAE-DA91-52A2-1D9DFD63CCEF 
  FPGA Name              :  
  JTAG ID Code           : 0x14b7d093 
  DDR Size               : 0 Bytes
  DDR Count              : 0 
  Mig Calibrated         : true 
  P2P Status             : disabled 
  P2P IO space required  : 32 GB

Clocks
  DATA_CLK (Data)        : 300 MHz
  KERNEL_CLK (Kernel)    : 500 MHz
  hbm_aclk (System)      : 450 MHz

Mac Addresses            : 00:0A:35:0D:F9:F8
                         : 00:0A:35:0D:F9:F9
                         : 00:0A:35:0D:F9:FA
                         : 00:0A:35:0D:F9:FB
                         : 00:0A:35:0D:F9:FC
                         : 00:0A:35:0D:F9:FD
                         : 00:0A:35:0D:F9:FE
                         : 00:0A:35:0D:F9:FF

Documentation impact (if any)

N/A