checkpatch: fix stringification macro defect

Fix checkpatch misreporting defect with stringification macros

ERROR: Macros with complex values should be enclosed in parenthesis
  #27: FILE: arch/arm/include/asm/kgdb.h:41:
  +#define ___to_string(X) #X
Signed-off-by: Joe Perches <joe@perches.com>
Reported-by: Vincent Stehlé <v-stehle@ti.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

scripts/checkpatch.pl

@@ -3016,6 +3016,7 @@ sub process {
 			    $dstat !~ /^'X'$/ &&					# character constants
 			    $dstat !~ /$exceptions/ &&
 			    $dstat !~ /^\.$Ident\s*=/ &&				# .foo =
+			    $dstat !~ /^(?:\#\s*$Ident|\#\s*$Constant)\s*$/ &&		# stringification #foo
 			    $dstat !~ /^do\s*$Constant\s*while\s*$Constant;?$/ &&	# do {...} while (...); // do {...} while (...)
 			    $dstat !~ /^for\s*$Constant$/ &&				# for (...)
 			    $dstat !~ /^for\s*$Constant\s+(?:$Ident|-?$Constant)$/ &&	# for (...) bar()