Escape ((…)) in AsciiDoc to fix broken example

Escape ((…)) in AsciiDoc to fix broken example

In AsciiDoc, double parentheses are used to mark flow index terms, but in this document, their use is intended to be interpreted by the shell's arithmetic expansion.  By escaping them with a backslash in the AsciiDoc, they pass through as-is to the manpage and other targets.

So, instead of a rendered result of `dd if=~/wipefs-sdb-0x00000438.bak of=/dev/sdb seek=$0x00000438 bs=1 conv=notrunc`, we get `dd if=~/wipefs-sdb-0x00000438.bak of=/dev/sdb seek=$((0x00000438)) bs=1 conv=notrunc`.

Seperately, when interpreted by a shell's arithmetic expansion, the 0x00000438 hex is converted to decimal 1080 `dd if=~/wipefs-sdb-0x00000438.bak of=/dev/sdb seek=1080 bs=1 conv=notrunc`