btrfs: Replace deprecated strncpy() with strscpy_pad()

strncpy() is deprecated for NUL-terminated destination buffers. Use
strscpy_pad() instead and don't zero-initialize the param array.

Compile-tested only.

Link: KSPP#90
Cc: linux-hardening@vger.kernel.org
Signed-off-by: Thorsten Blum <thorsten.blum@linux.dev>

fs/btrfs/sysfs.c

@@ -1330,13 +1330,13 @@ MODULE_PARM_DESC(read_policy,
 
 int btrfs_read_policy_to_enum(const char *str, s64 *value_ret)
 {
-	char param[32] = { 0 };
+	char param[32];
 	char __maybe_unused *value_str;
 
 	if (!str || strlen(str) == 0)
 		return 0;
 
-	strncpy(param, str, sizeof(param) - 1);
+	strscpy_pad(param, str);
 
 #ifdef CONFIG_BTRFS_EXPERIMENTAL
 	/* Separate value from input in policy:value format. */