hw/nand.c: correct the sense of the BUSY/READY status bit

The BIT6 of Status Register(SR):

SR[6] behaves the same as R/B# pin
    SR[6] = 0 indicates the device is busy;
    SR[6] = 1 means the device is ready

Some NAND flash controller (i.e. ftnandc021) relies on the SR[6]
to determine if the NAND flash erase/program is success or error timeout.

P.S:
The exmaple NAND flash datasheet could be found at following link:
http://www.mxic.com.tw/QuickPlace/hq/PageLibrary4825740B00298A3B.nsf/h_Index/8FEA549237D2F7674825795800104C26/$File/MX30LF1G08AA,%203V,%201Gb,%20v1.1.pdfSigned-off-by: NKuo-Jung Su <dantesu@gmail.com>
Reviewed-by: NPeter Crosthwaite <peter.crosthwaite@xilinx.com>
Signed-off-by: NEdgar E. Iglesias <edgar.iglesias@gmail.com>

hw/nand.c

@@ -46,7 +46,7 @@
 # define NAND_IOSTATUS_PLANE1	(1 << 2)
 # define NAND_IOSTATUS_PLANE2	(1 << 3)
 # define NAND_IOSTATUS_PLANE3	(1 << 4)
-# define NAND_IOSTATUS_BUSY	(1 << 6)
+# define NAND_IOSTATUS_READY    (1 << 6)
 # define NAND_IOSTATUS_UNPROTCT	(1 << 7)
 
 # define MAX_PAGE		0x800
@@ -231,6 +231,7 @@ static void nand_reset(DeviceState *dev)
     s->iolen = 0;
     s->offset = 0;
     s->status &= NAND_IOSTATUS_UNPROTCT;
+    s->status |= NAND_IOSTATUS_READY;
 }
 
 static inline void nand_pushio_byte(NANDFlashState *s, uint8_t value)