checkpatch: improve MULTISTATEMENT_MACRO_USE_DO_WHILE test

The logic currrently misses macros that start with an if statement.

e.g.:    #define foo(bar)   if (bar) baz;

Add a test for macro content that starts with if

Link: http://lkml.kernel.org/r/a9d41aafe1673889caf1a9850208fb7fd74107a0.1491783914.git.joe@perches.com
Signed-off-by: Joe Perches <joe@perches.com>
Reported-by: Andreas Mohr <andi@lisas.de>
Original-patch-by: Alfonso Lima <alfonsolimaastor@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

scripts/checkpatch.pl

@@ -4849,8 +4849,10 @@ sub process {
 			    $dstat !~ /^\(\{/ &&						# ({...
 			    $ctx !~ /^.\s*#\s*define\s+TRACE_(?:SYSTEM|INCLUDE_FILE|INCLUDE_PATH)\b/)
 			{
-
-				if ($dstat =~ /;/) {
+				if ($dstat =~ /^\s*if\b/) {
+					ERROR("MULTISTATEMENT_MACRO_USE_DO_WHILE",
+					      "Macros starting with if should be enclosed by a do - while loop to avoid possible if/else logic defects\n" . "$herectx");
+				} elsif ($dstat =~ /;/) {
 					ERROR("MULTISTATEMENT_MACRO_USE_DO_WHILE",
 					      "Macros with multiple statements should be enclosed in a do - while loop\n" . "$herectx");
 				} else {