modpost: Fix resource leak in read_dump()

Function read_dump() memory maps the input via grab_file(), but fails to call
the corresponding unmap function. Add the missing call to release_file().
Detected by Coverity: CID 1192419
Signed-off-by: Christian Engelmayer <cengelma@gmx.at>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

scripts/mod/modpost.c

@@ -2113,8 +2113,10 @@ static void read_dump(const char *fname, unsigned int kernel)
 		s->preloaded = 1;
 		sym_update_crc(symname, mod, crc, export_no(export));
 	}
+	release_file(file, size);
 	return;
 fail:
+	release_file(file, size);
 	fatal("parse error in symbol dump file\n");
 }