[PATCH] hostap: use offsetof() instead of own equivalent

The original macros result in gcc 4.2 warning about "cast from pointer
to integer of different size" on 64-bit systems.

Use of offsetof() on fields in substructures is widespread throughout
the kernel code and should work whether offsetof() is defined using
__compiler_offsetof() or a cast.
Signed-off-by: NPavel Roskin <proski@gnu.org>
Signed-off-by: NJohn W. Linville <linville@tuxdriver.com>

drivers/net/wireless/hostap/hostap_common.h

@@ -368,9 +368,9 @@ enum {
 
 #define PRISM2_HOSTAPD_MAX_BUF_SIZE 1024
 #define PRISM2_HOSTAPD_RID_HDR_LEN \
-((int) (&((struct prism2_hostapd_param *) 0)->u.rid.data))
+offsetof(struct prism2_hostapd_param, u.rid.data)
 #define PRISM2_HOSTAPD_GENERIC_ELEMENT_HDR_LEN \
-((int) (&((struct prism2_hostapd_param *) 0)->u.generic_elem.data))
+offsetof(struct prism2_hostapd_param, u.generic_elem.data)
 
 /* Maximum length for algorithm names (-1 for nul termination) used in ioctl()
  */