btrfs: make btrfs_find_contiguous_extent_bit() return bool instead of int

btrfs: make btrfs_find_contiguous_extent_bit() return bool instead of int

The function needs only to return true or false, so there's no need to
return an integer. Currently it returns 0 when a range with the given
bits is set and 1 when not found, which is a bit counter intuitive too.
So change the function to return a bool instead, returning true when a
range is found and false otherwise. Update the function's documentation
to mention the return value too.

Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Signed-off-by: Filipe Manana <fdmanana@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>