spi: tools: enable CROSS_COMPILE in Makefile

Signed-off-by: NJorge Ramirez-Ortiz <jorge.ramirez-ortiz@linaro.org>
Signed-off-by: NMark Brown <broonie@kernel.org>

tools/spi/Makefile

+CC = $(CROSS_COMPILE)gcc
+
 all: spidev_test spidev_fdx
 
 clean: