staging: fpgaboot: fix coccinelle warnings

drivers/staging/gs_fpgaboot/gs_fpgaboot.c:305:1-3: WARNING: PTR_RET can be used

 Use PTR_ERR_OR_ZERO rather than if(IS_ERR(...)) + PTR_ERR

Generated by: coccinelle/api/ptr_ret.cocci

CC: Insop Song <insop.song@gainspeed.com>
Signed-off-by: Fengguang Wu <fengguang.wu@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/gs_fpgaboot/gs_fpgaboot.c

@@ -302,10 +302,7 @@ static int init_driver(void)
 {
 	firmware_pdev = platform_device_register_simple("fpgaboot", -1,
 							 NULL, 0);
-	if (IS_ERR(firmware_pdev))
-		return PTR_ERR(firmware_pdev);
-
-	return 0;
+	return PTR_ERR_OR_ZERO(firmware_pdev);
 }
 
 static void finish_driver(void)