staging: iio: accel: Use __be16 instead of u16

This patch fixes these warning messages found by sparse:
drivers/staging/iio/accel/sca3000_ring.c:120:61: warning: incorrect type in argument 1 (different base types)
drivers/staging/iio/accel/sca3000_ring.c:120:61:    expected restricted __be16 const [usertype] *p
drivers/staging/iio/accel/sca3000_ring.c:120:61:    got unsigned short [usertype] *

Signed-off-by: Aybuke Ozdemir <aybuke.147@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>