meta-phosphor: image_version: update deprecated python function

The configparser library has deprecated the `readfp` function since
Python 3.2.  I observed that the `log.do_generate_phosphor_manifest`
had the following warning:

```
meta-phosphor/classes/image_version.bbclass:17: DeprecationWarning: This method will be removed in Python 3.12. Use 'parser.read_file()' instead.
```

The `read_file` is an identical replacement for `readfp` and has been
present since Python 3.2.

Signed-off-by: Patrick Williams <patrick@stwcx.xyz>
Change-Id: Ifd2f6ca5b1ff46bb351a024186515da28f13304d
diff --git a/meta-phosphor/classes/image_version.bbclass b/meta-phosphor/classes/image_version.bbclass
index e10bcd7..5462323 100644
--- a/meta-phosphor/classes/image_version.bbclass
+++ b/meta-phosphor/classes/image_version.bbclass
@@ -14,7 +14,7 @@
         with open(path, 'r') as fd:
             buf = '[root]\n' + fd.read()
             fd = io.StringIO(buf)
-            parser.readfp(fd)
+            parser.read_file(fd)
             value = parser['root'][key]
     except:
         pass