clang-tidy: Fix readability-isolate-declaration diagnostics

For example:

```
/usr/bin/clang-tidy -checks=-*, readability-isolate-declaration -export-fixes /tmp/tmpcxe3bcdw/tmpedwgdqvr.yaml -p=build /mnt/host/andrew/src/openbmc/libpldm/src/bios_table.c
/mnt/host/andrew/src/openbmc/libpldm/build/../src/bios_table.c:1093:2: error: multiple declarations in a single statement reduces readability [readability-isolate-declaration,-warnings-as-errors]
        const struct pldm_bios_attr_val_table_entry *tmp, *to_update = entry;
        ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/mnt/host/andrew/src/openbmc/libpldm/build/../src/bios_table.c:1094:2: error: multiple declarations in a single statement reduces readability [readability-isolate-declaration,-warnings-as-errors]
        size_t buffer_length = *dest_length, copied_length = 0, length = 0;
        ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
```

Signed-off-by: Andrew Jeffery <andrew@aj.id.au>
Change-Id: Ib866f2b36944c77dafcfbd3484a442444466f973
diff --git a/src/bios_table.c b/src/bios_table.c
index e8a419c..e9e1f3f 100644
--- a/src/bios_table.c
+++ b/src/bios_table.c
@@ -1090,8 +1090,11 @@
 	    src_table, src_length, PLDM_BIOS_ATTR_VAL_TABLE);
 
 	int rc = PLDM_SUCCESS;
-	const struct pldm_bios_attr_val_table_entry *tmp, *to_update = entry;
-	size_t buffer_length = *dest_length, copied_length = 0, length = 0;
+	const struct pldm_bios_attr_val_table_entry *tmp;
+	const struct pldm_bios_attr_val_table_entry *to_update = entry;
+	size_t buffer_length = *dest_length;
+	size_t copied_length = 0;
+	size_t length = 0;
 	while (!pldm_bios_table_iter_is_end(iter)) {
 		tmp = pldm_bios_table_iter_attr_value_entry_value(iter);
 		length = attr_value_table_entry_length(tmp);