spi/dw_spi: fix missing export of dw_spi_remove_host

So that interface drivers could be built as modules

Signed-off-by: Feng Tang <feng.tang@intel.com>
Signed-off-by: Grant Likely <grant.likely@secretlab.ca>
diff --git a/drivers/spi/dw_spi.c b/drivers/spi/dw_spi.c
index e434320..8ed38f1 100644
--- a/drivers/spi/dw_spi.c
+++ b/drivers/spi/dw_spi.c
@@ -957,6 +957,7 @@
 	/* Disconnect from the SPI framework */
 	spi_unregister_master(dws->master);
 }
+EXPORT_SYMBOL(dw_spi_remove_host);
 
 int dw_spi_suspend_host(struct dw_spi *dws)
 {