checkpatch: ensure we actually detect if assignments split across lines

When checking for assignments within if conditionals we check the whole of
the condition, but the match is performed using a line constrained regular
expression.  This means we can miss split conditionals or those on the
second line.  Allow the check to span lines.
Signed-off-by: Andy Whitcroft <apw@canonical.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

scripts/checkpatch.pl

@@ -2048,7 +2048,7 @@ sub process {
 		    $line =~ /\b(?:if|while|for)\s*\(/ && $line !~ /^.\s*#/) {
 			my ($s, $c) = ($stat, $cond);
 
-			if ($c =~ /\bif\s*\(.*[^<>!=]=[^=].*/) {
+			if ($c =~ /\bif\s*\(.*[^<>!=]=[^=].*/s) {
 				ERROR("do not use assignment in if condition\n" . $herecurr);
 			}