phosphor-regulators: journal: Fix some warnings by cppcheck

Warning message:
phosphor-regulators/src/journal.cpp:46:5: style: Class
'JournalCloser' has a constructor with 1 argument that is not
explicit. [noExplicitConstructor]
    JournalCloser(sd_journal* journal) : journal{journal}
    ^

Tested: Verify that there are no such warnings in local CI.

Signed-off-by: George Liu <liuxiwei@inspur.com>
Change-Id: I051ffc4905b64ef579b1eb58eac351967a5c6af1
diff --git a/phosphor-regulators/src/journal.cpp b/phosphor-regulators/src/journal.cpp
index eed5a70..955792a 100644
--- a/phosphor-regulators/src/journal.cpp
+++ b/phosphor-regulators/src/journal.cpp
@@ -43,7 +43,7 @@
     JournalCloser& operator=(const JournalCloser&) = delete;
     JournalCloser& operator=(JournalCloser&&) = delete;
 
-    JournalCloser(sd_journal* journal) : journal{journal}
+    explicit JournalCloser(sd_journal* journal) : journal{journal}
     {}
 
     ~JournalCloser()