staging: iio: ad5933: use sysfs_emit() in show functions

staging: iio: ad5933: use sysfs_emit() in show functions

Replace sprintf() with sysfs_emit() in all sysfs attribute show
functions. sysfs_emit() is the preferred API for sysfs callbacks as
it is aware of the PAGE_SIZE buffer limit.

Also remove the unnecessary (int) cast in ad5933_show_frequency()
and use the correct format specifier %llu for the unsigned long long
freqreg variable.

Signed-off-by: Gabriel Rondon <grondon@gmail.com>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>