checkpatch.pl: Add 'printf' to logFunctions

Signed-off-by: Tom Rini <trini@ti.com>

tools/checkpatch.pl

@@ -273,6 +273,7 @@ our $logFunctions = qr{(?x:
 	WARN(?:_RATELIMIT|_ONCE|)|
 	panic|
 	debug|
+	printf|
 	MODULE_[A-Z_]+
 )};