staging: iio: accel: change uint8_t to u8

This patch changes uint8_t type to preferred kernel
type u8 in order to follow the linux coding style
conventions.

Signed-off-by: Ioana Ciornei <ciorneiioana@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>