docs: filesystems: sysfs: Recommend sysfs_emit() for new code only

docs: filesystems: sysfs: Recommend sysfs_emit() for new code only

The advantages of converting existing sysfs show() methods to sysfs_emit()
and sysfs_emit_at() do not outweigh the risk of introducing bugs. Hence
recommend sysfs_emit() and sysfs_emit_at() only for new implementations of
show() methods.

Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: James Bottomley <James.Bottomley@HansenPartnership.com>
Cc: Martin K. Petersen <martin.petersen@oracle.com>
Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Reviewed-by: Martin K. Petersen <martin.petersen@oracle.com>
Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Link: https://lore.kernel.org/r/20250724153449.2433395-1-bvanassche@acm.org