show platform show mlnx option on non mlnx platform

[lguohan]

Description

Steps to reproduce the issue
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Describe the results you received

root@sonic:/# show platform
Usage: show platform [OPTIONS] COMMAND [ARGS]...

 Show platform-specific hardware info

Options:
 -?, -h, --help  Show this message and exit.

Commands:
 mlnx       Mellanox platform specific configuration...
 psustatus  Show PSU status information
 summary    Show hardware platform information
 syseeprom  Show system EEPROM information
i'm on a dell with tomahawk and i see mlnx option in the cmd line?

Describe the results you expected

Additional information you deem important (e.g. issue happens only occasionally)

Output of show version

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