doc: printk-formats: fix format specifier to %p[Ii]4[hnbl]

This might have been an oversight, as '4' is needed as %pI4/%pi4
are format specifiers and [hnbl] are extensions of it.
Signed-off-by: NDaniel Borkmann <dborkman@redhat.com>
CC: Joe Perches <joe@perches.com>
Signed-off-by: NJiri Kosina <jkosina@suse.cz>

Documentation/printk-formats.txt

@@ -97,7 +97,7 @@ IPv4 addresses:
 
 	%pI4	1.2.3.4
 	%pi4	001.002.003.004
-	%p[Ii][hnbl]
+	%p[Ii]4[hnbl]
 
 	For printing IPv4 dot-separated decimal addresses. The 'I4' and 'i4'
 	specifiers result in a printed address with ('i4') or without ('I4')