iio: core: Use sysfs_emit()

iio: core: Use sysfs_emit()

sysfs_emit() is preferred over raw s*printf() for sysfs attributes since it
knows about the sysfs buffer specifics and has some built-in checks for
size and alignment.

This patch converts the places in the IIO core that follow the pattern of

   return s*printf(...)

to

   return sysfs_emit(...)

This covers the new places that have been introduced where sprintf() is
used for formatting sysfs output since the last time this was done in
commit 83ca56b663cf ("iio: core: Use sysfs_emit() (trivial bits)").

Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
Link: https://lore.kernel.org/r/20211216185217.1054495-2-lars@metafoo.de
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>