ewah: fix constness of ewah_read_mmap

Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

ewah/ewah_io.c

@@ -110,9 +110,9 @@ int ewah_serialize(struct ewah_bitmap *self, int fd)
 	return ewah_serialize_to(self, write_helper, (void *)(intptr_t)fd);
 }
 
-int ewah_read_mmap(struct ewah_bitmap *self, void *map, size_t len)
+int ewah_read_mmap(struct ewah_bitmap *self, const void *map, size_t len)
 {
-	uint8_t *ptr = map;
+	const uint8_t *ptr = map;
 	size_t i;
 
 	self->bit_size = get_be32(ptr);

ewah/ewok.h

@@ -99,7 +99,7 @@ int ewah_serialize(struct ewah_bitmap *self, int fd);
 int ewah_serialize_native(struct ewah_bitmap *self, int fd);
 
 int ewah_deserialize(struct ewah_bitmap *self, int fd);
-int ewah_read_mmap(struct ewah_bitmap *self, void *map, size_t len);
+int ewah_read_mmap(struct ewah_bitmap *self, const void *map, size_t len);
 int ewah_read_mmap_native(struct ewah_bitmap *self, void *map, size_t len);
 
 uint32_t ewah_checksum(struct ewah_bitmap *self);