Adjust strncpy sizes

When building under bitbake with the latest openbmc, we get compile
warnings such as these:

```
| ../git/sections/cper-section-nvidia.c: In function 'ir_section_nvidia_to_cper':
| ../git/sections/cper-section-nvidia.c:67:9: error: '__builtin_strncpy' specified bound 16 equals destination size [-Werror=stringop-truncation]
|    67 |         strncpy(section_cper->Signature,
```

Using `strncpy` on its own is unsafe because a string too long will
end up in the destination buffer without NUL termination.  Adjust
the strncpy to be one shorter than the buffer and force the trailing
byte to be a NUL.

Repeat this pattern for all `strncpy` calls.

Change-Id: I45c630733f0138d2b089a60f698d75e1c09de9e2
Signed-off-by: Patrick Williams <patrick@stwcx.xyz>
diff --git a/sections/cper-section-nvidia.c b/sections/cper-section-nvidia.c
index f0ccec6..e2f8aef 100644
--- a/sections/cper-section-nvidia.c
+++ b/sections/cper-section-nvidia.c
@@ -67,7 +67,8 @@
 	strncpy(section_cper->Signature,
 		json_object_get_string(
 			json_object_object_get(section, "signature")),
-		sizeof(section_cper->Signature));
+		sizeof(section_cper->Signature) - 1);
+	section_cper->Signature[sizeof(section_cper->Signature) - 1] = '\0';
 
 	//Fields.
 	section_cper->ErrorType = json_object_get_int(