powerpc/nvram: use kmemdup rather than duplicating its implementation

The patch was generated using fixed coccinelle semantic patch
scripts/coccinelle/api/memdup.cocci [1].

[1]: http://permalink.gmane.org/gmane.linux.kernel/2014320Signed-off-by: Andrzej Hajda <a.hajda@samsung.com>
Reviewed-by: Nathan Fontenot <nfont@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

arch/powerpc/kernel/nvram_64.c

@@ -541,10 +541,9 @@ static ssize_t nvram_pstore_read(u64 *id, enum pstore_type_id *type,
 			time->tv_sec = be64_to_cpu(oops_hdr->timestamp);
 			time->tv_nsec = 0;
 		}
-		*buf = kmalloc(length, GFP_KERNEL);
+		*buf = kmemdup(buff + hdr_size, length, GFP_KERNEL);
 		if (*buf == NULL)
 			return -ENOMEM;
-		memcpy(*buf, buff + hdr_size, length);
 		kfree(buff);
 
 		if (err_type == ERR_TYPE_KERNEL_PANIC_GZ)