x86, AMD IOMMU: remove unneeded initializations from command buffer allocation

This patch removes an unneeded initialization from the alloc_command_buffer
function and replaces a memset with __GFP_ZERO.

Signed-off-by: Joerg Roedel <joerg.roedel@amd.com>
Cc: iommu@lists.linux-foundation.org
Cc: bhavna.sarathy@amd.com
Cc: robert.richter@amd.com
Signed-off-by: Ingo Molnar <mingo@elte.hu>

arch/x86/kernel/amd_iommu_init.c

@@ -394,17 +394,15 @@ static int __init find_last_devid_acpi(struct acpi_table_header *table)
  */
 static u8 * __init alloc_command_buffer(struct amd_iommu *iommu)
 {
-	u8 *cmd_buf = (u8 *)__get_free_pages(GFP_KERNEL,
+	u8 *cmd_buf = (u8 *)__get_free_pages(GFP_KERNEL | __GFP_ZERO,
 			get_order(CMD_BUFFER_SIZE));
-	u64 entry = 0;
+	u64 entry;
 
 	if (cmd_buf == NULL)
 		return NULL;
 
 	iommu->cmd_buf_size = CMD_BUFFER_SIZE;
 
-	memset(cmd_buf, 0, CMD_BUFFER_SIZE);
-
 	entry = (u64)virt_to_phys(cmd_buf);
 	entry |= MMIO_CMD_SIZE_512;
 	memcpy_toio(iommu->mmio_base + MMIO_CMD_BUF_OFFSET,