fix taihu soft spi_read

The taihu board used gpio_read_out_bit which reads the output register and not
the pin state.

Signed-off-by: Markus Brunner <super.firetwister@gmail.com>
diff --git a/board/amcc/taihu/taihu.c b/board/amcc/taihu/taihu.c
index ea83671..eedde59 100644
--- a/board/amcc/taihu/taihu.c
+++ b/board/amcc/taihu/taihu.c
@@ -162,7 +162,7 @@
 
 unsigned char spi_read(void)
 {
-	return (unsigned char)gpio_read_out_bit(SPI_DIN_GPIO15);
+	return (unsigned char)gpio_read_in_bit(SPI_DIN_GPIO15);
 }
 
 void taihu_spi_chipsel(int cs)