staging: rtl8712: Replace FIELD_OFFSET() with offsetof()

Use the existing offsetof() macro instead of duplicating code.
Signed-off-by: Mauro Dreissig <mukadr@gmail.com>
Link: https://lore.kernel.org/r/20200701214420.5566-2-mukadr@gmail.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/rtl8712/basic_types.h

@@ -21,7 +21,6 @@
 
 #define SIZE_T __kernel_size_t
 #define sint signed int
-#define FIELD_OFFSET(s, field)	((addr_t)&((s *)(0))->field)
 
 /* Should we extend this to be host_addr_t and target_addr_t for case:
  *	host : x86_64

drivers/staging/rtl8712/hal_init.c

@@ -133,7 +133,7 @@ static u8 chk_fwhdr(struct fw_hdr *pfwhdr, u32 ulfilelength)
 	if (pfwhdr->fw_priv_sz != sizeof(struct fw_priv))
 		return _FAIL;
 	/* check fw_sz & image_fw_sz */
-	fwhdrsz = FIELD_OFFSET(struct fw_hdr, fwpriv) + pfwhdr->fw_priv_sz;
+	fwhdrsz = offsetof(struct fw_hdr, fwpriv) + pfwhdr->fw_priv_sz;
 	fw_sz =  fwhdrsz + pfwhdr->img_IMEM_size + pfwhdr->img_SRAM_size +
 		 pfwhdr->dmem_size;
 	if (fw_sz != ulfilelength)
@@ -173,7 +173,7 @@ static u8 rtl8712_dl_fw(struct _adapter *adapter)
 		txdesc = (struct tx_desc *)(tmpchar + FWBUFF_ALIGN_SZ -
 			    ((addr_t)(tmpchar) & (FWBUFF_ALIGN_SZ - 1)));
 		payload = (u8 *)(txdesc) + txdscp_sz;
-		ptr = (u8 *)mappedfw + FIELD_OFFSET(struct fw_hdr, fwpriv) +
+		ptr = (u8 *)mappedfw + offsetof(struct fw_hdr, fwpriv) +
 		      fwhdr.fw_priv_sz;
 		/* Download FirmWare */
 		/* 1. determine IMEM code size and Load IMEM Code Section */

drivers/staging/rtl8712/rtl871x_ioctl_linux.c

@@ -407,7 +407,7 @@ static int wpa_set_encryption(struct net_device *dev, struct ieee_param *param,
 			return -ENOMEM;
 		pwep->KeyLength = wep_key_len;
 		pwep->Length = wep_key_len +
-			FIELD_OFFSET(struct NDIS_802_11_WEP, KeyMaterial);
+			offsetof(struct NDIS_802_11_WEP, KeyMaterial);
 		if (wep_key_len == 13) {
 			padapter->securitypriv.PrivacyAlgrthm = _WEP104_;
 			padapter->securitypriv.XGrpPrivacy = _WEP104_;
@@ -1555,7 +1555,7 @@ static int r8711_wx_set_enc(struct net_device *dev,
 	if (erq->length > 0) {
 		wep.KeyLength = erq->length <= 5 ? 5 : 13;
 		wep.Length = wep.KeyLength +
-			     FIELD_OFFSET(struct NDIS_802_11_WEP, KeyMaterial);
+			     offsetof(struct NDIS_802_11_WEP, KeyMaterial);
 	} else {
 		wep.KeyLength = 0;
 		if (keyindex_provided == 1) { /* set key_id only, no given