Fixed build errors.

kernel/trace/trace_events_filter.c: In function "ftrace_function_set_filter_cb":
kernel/trace/trace_events_filter.c:2074:8: warning: "ret" may be used uninitialized in this function [-Wuninitialized]
Patch has been queued mainline commit 92d8d4a "tracing/filter: Add missing initialization

arch/arm/mach-bcm2708/bcm2708.c: In function "timer_set_mode":
arch/arm/mach-bcm2708/bcm2708.c:780:16: warning: unused variable "stc" [-Wunused-variable]
Removed unused variable.

drivers/usb/storage/realtek_cr.c: In function "init_realtek_cr":
drivers/usb/storage/realtek_cr.c:476:33: warning: "buf[15]" may be used uninitia
lized in this function [-Wuninitialized]
Change conditional.