hidapi/linux/hid.c: define BUS_SPI if not already defined.

src/hidapi/linux/hid.c

@@ -44,6 +44,10 @@
 
 #include "../hidapi/hidapi.h"
 
+#ifndef BUS_SPI
+#define BUS_SPI 0x1C
+#endif
+
 #ifdef HIDAPI_ALLOW_BUILD_WORKAROUND_KERNEL_2_6_39
 /* This definitions first appeared in Linux Kernel 2.6.39 in linux/hidraw.h.
     hidapi doesn't support kernels older than that,