lib: rhashtable - Remove weird non-ASCII characters from comments

My editor spewed garbage that looked like memory corruption on
my screen.  It turns out that a number of occurences of "fi" got
turned into a ligature.

This patch replaces these ligatures with the ASCII letters "fi".

Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

Cheers,
Acked-by: Thomas Graf <tgraf@suug.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>