s390/iucv: Convert sprintf/snprintf to scnprintf

s390/iucv: Convert sprintf/snprintf to scnprintf

Convert sprintf/snprintf calls to scnprintf to better align with the
kernel development community practices [1].

Link: https://lwn.net/Articles/69419
Reviewed-by: Alexandra Winter <wintera@linux.ibm.com>
Signed-off-by: Aswin Karuvally <aswin@linux.ibm.com>
Signed-off-by: Alexandra Winter <wintera@linux.ibm.com>
Reviewed-by: Simon Horman <horms@kernel.org>
Link: https://patch.msgid.link/20251017094954.1402684-1-wintera@linux.ibm.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>