[FS#423] Linksys WRT1900ACS USB led names are wrong

[LEDE Bugs]

The following task has a new comment added:

FS#423 - Linksys WRT1900ACS USB led names are wrong
User who did this - howl (howl)

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The renaming should be as follow:
USB2 -> USB1
USB3 -> USB2
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More information can be found at the following URL:
https://bugs.lede-project.org/index.php?do=details&task_id=423#comment1373