[PATCH] checkpatch: Fix ignoring cover-letter logic

[Stafford Horne <shorne@gmail.com>]

Currently running checkpatch on a directory with a cover-letter.patch
file reports the following error:

  -----------------------------------------
  patches/smp-v2/v2-0000-cover-letter.patch
  -----------------------------------------

  ERROR: Does not appear to be a unified-diff format patch

The logic to suppress the unified-diff check for cover letters is there
but is checking $file instead of $filename.  Fix the variable to use the
correct one.

Signed-off-by: Stafford Horne <shorne@gmail.com>
---
 scripts/checkpatch.pl | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/scripts/checkpatch.pl b/scripts/checkpatch.pl
index 2287a0bca863..9e46986e06b8 100755
--- a/scripts/checkpatch.pl
+++ b/scripts/checkpatch.pl
@@ -6365,7 +6365,7 @@ sub process {
 		exit(0);
 	}
 
-	if (!$is_patch && $file !~ /cover-letter\.patch$/) {
+	if (!$is_patch && $filename !~ /cover-letter\.patch$/) {
 		ERROR("NOT_UNIFIED_DIFF",
 		      "Does not appear to be a unified-diff format patch\n");
 	}
-- 
2.13.5