CVE-2024-42158 s390/pkey: Use kfree_sensitive() to fix Coccinelle warnings

In the Linux kernel, the following vulnerability has been resolved:

s390/pkey: Use kfree_sensitive() to fix Coccinelle warnings

Replace memzero_explicit() and kfree() with kfree_sensitive() to fix
warnings reported by Coccinelle:

WARNING opportunity for kfree_sensitive/kvfree_sensitive (line 1506)
WARNING opportunity for kfree_sensitive/kvfree_sensitive (line 1643)
WARNING opportunity for kfree_sensitive/kvfree_sensitive (line 1770)