m68k: Use sizeof_field() helper

Make use of the sizeof_field() helper instead of an open-coded version.
Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
Link: https://lore.kernel.org/r/20200527133942.GA10408@embeddedorSigned-off-by: Geert Uytterhoeven <geert@linux-m68k.org>

arch/m68k/kernel/signal.c

@@ -61,25 +61,25 @@
 #define	FMT4SIZE	0
 #else
 #define	FORMAT		0
-#define	FMT4SIZE	sizeof(((struct frame *)0)->un.fmt4)
+#define	FMT4SIZE	sizeof_field(struct frame, un.fmt4)
 #endif
 
 static const int frame_size_change[16] = {
-  [1]	= -1, /* sizeof(((struct frame *)0)->un.fmt1), */
-  [2]	= sizeof(((struct frame *)0)->un.fmt2),
-  [3]	= sizeof(((struct frame *)0)->un.fmt3),
+  [1]	= -1, /* sizeof_field(struct frame, un.fmt1), */
+  [2]	= sizeof_field(struct frame, un.fmt2),
+  [3]	= sizeof_field(struct frame, un.fmt3),
   [4]	= FMT4SIZE,
-  [5]	= -1, /* sizeof(((struct frame *)0)->un.fmt5), */
-  [6]	= -1, /* sizeof(((struct frame *)0)->un.fmt6), */
-  [7]	= sizeof(((struct frame *)0)->un.fmt7),
-  [8]	= -1, /* sizeof(((struct frame *)0)->un.fmt8), */
-  [9]	= sizeof(((struct frame *)0)->un.fmt9),
-  [10]	= sizeof(((struct frame *)0)->un.fmta),
-  [11]	= sizeof(((struct frame *)0)->un.fmtb),
-  [12]	= -1, /* sizeof(((struct frame *)0)->un.fmtc), */
-  [13]	= -1, /* sizeof(((struct frame *)0)->un.fmtd), */
-  [14]	= -1, /* sizeof(((struct frame *)0)->un.fmte), */
-  [15]	= -1, /* sizeof(((struct frame *)0)->un.fmtf), */
+  [5]	= -1, /* sizeof_field(struct frame, un.fmt5), */
+  [6]	= -1, /* sizeof_field(struct frame, un.fmt6), */
+  [7]	= sizeof_field(struct frame, un.fmt7),
+  [8]	= -1, /* sizeof_field(struct frame, un.fmt8), */
+  [9]	= sizeof_field(struct frame, un.fmt9),
+  [10]	= sizeof_field(struct frame, un.fmta),
+  [11]	= sizeof_field(struct frame, un.fmtb),
+  [12]	= -1, /* sizeof_field(struct frame, un.fmtc), */
+  [13]	= -1, /* sizeof_field(struct frame, un.fmtd), */
+  [14]	= -1, /* sizeof_field(struct frame, un.fmte), */
+  [15]	= -1, /* sizeof_field(struct frame, un.fmtf), */
 };
 
 static inline int frame_extra_sizes(int f)
@@ -651,7 +651,7 @@ static int mangle_kernel_stack(struct pt_regs *regs, int formatvec,
 	} else {
 		struct switch_stack *sw = (struct switch_stack *)regs - 1;
 		/* yes, twice as much as max(sizeof(frame.un.fmt<x>)) */
-		unsigned long buf[sizeof(((struct frame *)0)->un) / 2];
+		unsigned long buf[sizeof_field(struct frame, un) / 2];
 
 		/* that'll make sure that expansion won't crap over data */
 		if (copy_from_user(buf + fsize / 4, fp, fsize))