[PATCH] readahead: reset cache_hit earlier

We don't reset the cache hit count until after readahead does a successful
readahead.  This seems to leave a corner case open where we miss in cache,
but don't restart the readhead right away.

Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>