tools: usb: ffs-test: switch to _DEFAULT_SOURCE

_BSD_SOURCE is deprecated and gives a build warning. Let's use
_DEFAULT_SOURCE instead.
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>

tools/usb/ffs-test.c

@@ -22,7 +22,7 @@
 /* $(CROSS_COMPILE)cc -Wall -Wextra -g -o ffs-test ffs-test.c -lpthread */
 
 
-#define _BSD_SOURCE /* for endian.h */
+#define _DEFAULT_SOURCE /* for endian.h */
 
 #include <endian.h>
 #include <errno.h>