GPT: incomplete initialization in allocate_disk_part

memset(newpart, '\0', sizeof(newpart));
only initializes the firest 4 or 8 bytes of *newpart and not the whole
structure disk_part.

We should use sizeof(struct disk_part).

Instead of malloc and memset we can use calloc.

Identified by cppcheck.

Fixes: 09a49930 GPT: read partition table from device into a data structure
Reported-by: Coverity (CID: 167228)
Cc: Stefan Roese <sr@denx.de>
Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>
Reviewed-by: Stefan Roese <sr@denx.de>
Reviewed-by: Simon Glass <sjg@chromium.org>

cmd/gpt.c

@@ -190,10 +190,9 @@ static void del_gpt_info(void)
 static struct disk_part *allocate_disk_part(disk_partition_t *info, int partnum)
 {
 	struct disk_part *newpart;
-	newpart = malloc(sizeof(*newpart));
+	newpart = calloc(1, sizeof(struct disk_part));
 	if (!newpart)
 		return ERR_PTR(-ENOMEM);
-	memset(newpart, '\0', sizeof(newpart));
 
 	newpart->gpt_part_info.start = info->start;
 	newpart->gpt_part_info.size = info->size;