procd: fix build when DEBUG is set

procd: fix build when DEBUG is set

There is a collision between the DEBUG set in the CMake file as
flag and the macro defined in log.h, resulting in build error:

In file included from ./procd/initd/init.h:19:0,
                 from ./procd/initd/init.c:33:
./procd/initd/../log.h:20:0: error: "DEBUG" redefined [-Werror]
 #define DEBUG(level, fmt, ...) do { \
 ^
<command-line>:0:0: note: this is the location of the previous definition
cc1: all warnings being treated as errors

This patch fixes the issue by renaming the build flag to
UDEV_DEBUG (since it is only used in udevtrigger).

Signed-off-by: Zefir Kurtisi <zefir.kurtisi@neratec.com>