spi/dw_spi: fix missing export of dw_spi_remove_host

So that interface drivers could be built as modules
Signed-off-by: NFeng Tang <feng.tang@intel.com>
Signed-off-by: NGrant Likely <grant.likely@secretlab.ca>

drivers/spi/dw_spi.c

@@ -957,6 +957,7 @@ void __devexit dw_spi_remove_host(struct dw_spi *dws)
 	/* 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)
 {