staging:iio:resolver:ad2s1210 fix negative IIO_ANGL_VEL read

gcc-7 points out an older regression:

drivers/staging/iio/resolver/ad2s1210.c: In function 'ad2s1210_read_raw':
drivers/staging/iio/resolver/ad2s1210.c:515:42: error: '<<' in boolean context, did you mean '<' ? [-Werror=int-in-bool-context]

The original code had 'unsigned short' here, but incorrectly got
converted to 'bool'. This reverts the regression and uses a normal
type instead.

Fixes: 2914854 ("staging:iio:resolver:ad2s1210 minimal chan spec conversion.")
Cc: stable@vger.kernel.org
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

drivers/staging/iio/resolver/ad2s1210.c

@@ -472,7 +472,7 @@ static int ad2s1210_read_raw(struct iio_dev *indio_dev,
 			     long m)
 {
 	struct ad2s1210_state *st = iio_priv(indio_dev);
-	bool negative;
+	u16 negative;
 	int ret = 0;
 	u16 pos;
 	s16 vel;