[Bug-ddrescue] minor documentation bug: '--retry-passes' should be '--retries'

[Robert Trevellyan]

The online manual at
https://www.gnu.org/software/ddrescue/manual/ddrescue_manual.html shows the
option
'--retry-passes=n'
but the program actually accepts
'--retries=n'
as indicated when invoking the program with '--help'.

Thanks for developing and maintaining this excellent tool. One lady thought
she had lost all her photos of her son growing up, but ddrescue recovered
everything.