[media] coda: remove extraneous TRACE_SYSTEM_STRING

The coda tracing code causes lots of warnings like

In file included from /git/arm-soc/include/trace/define_trace.h:90:0,
                 from /git/arm-soc/drivers/media/platform/coda/trace.h:203,
                 from /git/arm-soc/drivers/media/platform/coda/coda-bit.c:34:
/git/arm-soc/include/trace/ftrace.h:28:0: warning: "TRACE_SYSTEM_STRING" redefined
 #define TRACE_SYSTEM_STRING __app(TRACE_SYSTEM_VAR,__trace_system_name)
 ^
In file included from /git/arm-soc/include/trace/define_trace.h:83:0,
                 from /git/arm-soc/drivers/media/platform/coda/trace.h:203,
                 from /git/arm-soc/drivers/media/platform/coda/coda-bit.c:34:
/git/arm-soc/drivers/media/platform/coda/./trace.h:12:0: note: this is the location of the previous definition
 #define TRACE_SYSTEM_STRING __stringify(TRACE_SYSTEM)

>From what I can tell, this is just the result of a bogus TRACE_SYSTEM_STRING
definition, and removing that one makes the warnings go away.

Fixes: 9a1a8f99 ("[media] coda: Add tracing support")

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Philipp Zabel <p.zabel@pengutronix.de>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>