checkpatch: add fix option for ASSIGNMENT_CONTINUATIONS

Currently, checkpatch warns us if an assignment operator is placed at the
start of a line and not at the end of previous line.

E.g., running checkpatch on commit 8195b139 ("hv_netvsc: fix
deadlock on hotplug") reports:

  CHECK: Assignment operator '=' should be on the previous line
  +	struct netvsc_device *nvdev
  +		= container_of(w, struct netvsc_device, subchan_work);

Provide a simple fix by appending assignment operator to the previous
line and removing from the current line, if both the lines are additions
(ie start with '+')

Link: https://lkml.kernel.org/r/20201121120407.22942-1-yashsri421@gmail.comSigned-off-by: Aditya Srivastava <yashsri421@gmail.com>
Acked-by: Joe Perches <joe@perches.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

scripts/checkpatch.pl

@@ -3533,8 +3533,14 @@ sub process {
 
 # check for assignments on the start of a line
 		if ($sline =~ /^\+\s+($Assignment)[^=]/) {
-			CHK("ASSIGNMENT_CONTINUATIONS",
-			    "Assignment operator '$1' should be on the previous line\n" . $hereprev);
+			my $operator = $1;
+			if (CHK("ASSIGNMENT_CONTINUATIONS",
+				"Assignment operator '$1' should be on the previous line\n" . $hereprev) &&
+			    $fix && $prevrawline =~ /^\+/) {
+				# add assignment operator to the previous line, remove from current line
+				$fixed[$fixlinenr - 1] .= " $operator";
+				$fixed[$fixlinenr] =~ s/\Q$operator\E\s*//;
+			}
 		}
 
 # check for && or || at the start of a line