scripts/get_maintainer.pl: change "die" to "warn" when command line file is not a patch

fixes git send-email with a cover letter

Signed-off-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/get_maintainer.pl

@@ -165,7 +165,7 @@ foreach my $file (@ARGV) {
 	}
 	close(PATCH);
 	if ($file_cnt == @files) {
-	    die "$P: file '${file}' doesn't appear to be a patch.  "
+	    warn "$P: file '${file}' doesn't appear to be a patch.  "
 		. "Add -f to options?\n";
 	}
 	@files = sort_and_uniq(@files);