spi: export tracepoint symbols to modules

The newly added tracepoints in the spi-mxs driver cause a link
error when the driver is a loadable module:

ERROR: "__tracepoint_spi_transfer_stop" [drivers/spi/spi-mxs.ko] undefined!
ERROR: "__tracepoint_spi_transfer_start" [drivers/spi/spi-mxs.ko] undefined!

I'm not quite sure where to put the export statements, but
directly after the inclusion of the header seems as good as
any other place.

Fixes: f3fdea3af4 ("spi: mxs: add tracing to custom .transfer_one_message callback")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Mark Brown <broonie@kernel.org>

drivers/spi/spi.c

@@ -36,6 +36,8 @@
 
 #define CREATE_TRACE_POINTS
 #include <trace/events/spi.h>
+EXPORT_TRACEPOINT_SYMBOL(spi_transfer_start);
+EXPORT_TRACEPOINT_SYMBOL(spi_transfer_stop);
 
 #include "internals.h"