staging:iio: replace rip_lots naming with read_first_n

Change suggested by Arnd Bergmann, Related patch to remove
pointless (now) dead_offset parameter will have await
proper fix for the sca3000 driver.  That depends on
some intermediate patches so may be a little while.

Signed-off-by: Jonathan Cameron <jic23@cam.ac.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>