calloc: Use calloc() at most places

This modifies most of the places we do some form of:

  X = malloc(Y * Z);

to use calloc(Y, Z) instead.

Among other issues, this fixes:
  - allocation of integer overflow in grub_png_decode_image_header()
    reported by Chris Coulson,
  - allocation of integer overflow in luks_recover_key()
    reported by Chris Coulson,
  - allocation of integer overflow in grub_lvm_detect()
    reported by Chris Coulson.

Fixes: CVE-2020-14308

Signed-off-by: Peter Jones <pjones@redhat.com>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>

grub-core/video/capture.c

@@ -89,7 +89,7 @@ grub_video_capture_start (const struct grub_video_mode_info *mode_info,
   framebuffer.mode_info = *mode_info;
   framebuffer.mode_info.blit_format = grub_video_get_blit_format (&framebuffer.mode_info);
 
-  framebuffer.ptr = grub_malloc (framebuffer.mode_info.height * framebuffer.mode_info.pitch);
+  framebuffer.ptr = grub_calloc (framebuffer.mode_info.height, framebuffer.mode_info.pitch);
   if (!framebuffer.ptr)
     return grub_errno;