doc: filter_mod documentation inflation options out-of-date

[hkershaw-brown]

https://docs.dart.ucar.edu/en/latest/assimilation_code/modules/assimilation/filter_mod.html#inflation-options
"The value for the inf_flavor is a character string"

This was reverted in #321
inf_flavours are integers in the namelist.

edit: also in the table

inf_flavor	character(len=32), dimension(2)	Inflation flavor [prior, posterior] see Inflation Options below.

FYI for git historians, this documentation came in in the documentation conversion from html to rst
00fb59c
not in the pull request with the code change https://github.com/NCAR/DART/pull/154/files