ARM: fix write*() I/O accessors

Commit 3c0659b "ARM: Avoid compiler optimization for readb, writeb
and friends." introduced I/O accessors with memory barriers.
Unfortunately the new write*() accessors introduced a bug:

The problem is that the argument "v" gets evaluated twice.  This
breaks code like used here (from "drivers/net/dnet.c"):

	for (i = 0; i < wrsz; i++)
		writel(*bufp++, &dnet->regs->TX_DATA_FIFO);

Use auxiliary variables to avoid such problems.

Signed-off-by: Wolfgang Denk <wd@denx.de>
Cc: Albert Aribaud <albert.aribaud@free.fr>
Cc: Alexander Holler <holler@ahsoftware.de>
Cc: Dirk Behme <dirk.behme@googlemail.com>

arch/arm/include/asm/io.h

@@ -133,9 +133,9 @@ extern inline void __raw_readsl(unsigned int addr, void *data, int longlen)
 #define __iormb()	dmb()
 #define __iowmb()	dmb()
 
-#define writeb(v,c)	({ __iowmb(); __arch_putb(v,c); v; })
-#define writew(v,c)	({ __iowmb(); __arch_putw(v,c); v; })
-#define writel(v,c)	({ __iowmb(); __arch_putl(v,c); v; })
+#define writeb(v,c)	({ u8  __v = v; __iowmb(); __arch_putb(__v,c); __v; })
+#define writew(v,c)	({ u16 __v = v; __iowmb(); __arch_putw(__v,c); __v; })
+#define writel(v,c)	({ u32 __v = v; __iowmb(); __arch_putl(__v,c); __v; })
 
 #define readb(c)	({ u8  __v = __arch_getb(c); __iormb(); __v; })
 #define readw(c)	({ u16 __v = __arch_getw(c); __iormb(); __v; })