docs: filesystems: sysfs: Make text and code for ->show() consistent

The documentation says that ->show() should only use sysfs_emit() or
sysfs_emit_at(), but example keeps outdated code. Update the code to
be consistent.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Link: https://lore.kernel.org/r/20220928135741.54919-1-andriy.shevchenko@linux.intel.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>