get_maintainer.pl: find maintainers for removed files

For removed files, get_maintainer.pl doesn't find any maintainers (besides
the default [email protected]), as it only looks at the "+++"
lines, which are "/dev/null" for removals.  Fix this by extending the
parsing to the "---" lines.

E.g. for the two line test patch below the real score maintainers will now
be found:

    --- a/arch/score/include/asm/dma-mapping.h
    +++ /dev/null

Signed-off-by: Geert Uytterhoeven <[email protected]>
Cc: Joe Perches <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

scripts/get_maintainer.pl

@@ -433,7 +433,7 @@ sub read_mailmap {
 
 	while (<$patch>) {
 	    my $patch_line = $_;
-	    if (m/^\+\+\+\s+(\S+)/) {
+	    if (m/^\+\+\+\s+(\S+)/ or m/^---\s+(\S+)/) {
 		my $filename = $1;
 		$filename =~ s@^[^/]*/@@;
 		$filename =~ s@\n@@;