[ARM] Orion NAND: Make asm volatile avoid GCC pushing ldrd out of the loop

GCC 4.3.3 and 4.4.1 happily moves the dword load instruction out of the
loop in orion_nand_read_buf. This patch makes the instruction volatile
to avoid the issue. I've discussed this at gcc-help, refer to the thread
at

  http://gcc.gnu.org/ml/gcc-help/2009-08/msg00187.html

The early clobber is added to avoid the destination registers and the
source register overlapping.
Signed-off-by: Simon Kagstrom <simon.kagstrom@netinsight.net>
Signed-off-by: Nicolas Pitre <nico@marvell.com>

drivers/mtd/nand/orion_nand.c

@@ -61,7 +61,7 @@ static void orion_nand_read_buf(struct mtd_info *mtd, uint8_t *buf, int len)
 	buf64 = (uint64_t *)buf;
 	while (i < len/8) {
 		uint64_t x;
-		asm ("ldrd\t%0, [%1]" : "=r" (x) : "r" (io_base));
+		asm volatile ("ldrd\t%0, [%1]" : "=&r" (x) : "r" (io_base));
 		buf64[i++] = x;
 	}
 	i *= 8;