trace2: use designated initializers for "struct tr2_dst"

Convert the "static struct tr2_dst" assignments in trace2/* to use
designated initializers. I don't think it improves readability to
include the explicit 0-ing out of the
fd/initialized/need_close/too_many_files members, so let's have those
be initialized implicitly by the compiler.

Signed-off-by: Ævar Arnfjörð Bjarmason <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: avar

trace2/tr2_tgt_event.c

@@ -10,7 +10,9 @@
 #include "trace2/tr2_tgt.h"
 #include "trace2/tr2_tls.h"
 
-static struct tr2_dst tr2dst_event = { TR2_SYSENV_EVENT, 0, 0, 0, 0 };
+static struct tr2_dst tr2dst_event = {
+	.sysenv_var = TR2_SYSENV_EVENT,
+};
 
 /*
  * The version number of the JSON data generated by the EVENT target in this

trace2/tr2_tgt_normal.c

@@ -9,7 +9,9 @@
 #include "trace2/tr2_tgt.h"
 #include "trace2/tr2_tls.h"
 
-static struct tr2_dst tr2dst_normal = { TR2_SYSENV_NORMAL, 0, 0, 0, 0 };
+static struct tr2_dst tr2dst_normal = {
+	.sysenv_var = TR2_SYSENV_NORMAL,
+};
 
 /*
  * Use the TR2_SYSENV_NORMAL_BRIEF setting to omit the "<time> <file>:<line>"

trace2/tr2_tgt_perf.c

@@ -11,7 +11,9 @@
 #include "trace2/tr2_tgt.h"
 #include "trace2/tr2_tls.h"
 
-static struct tr2_dst tr2dst_perf = { TR2_SYSENV_PERF, 0, 0, 0, 0 };
+static struct tr2_dst tr2dst_perf = {
+	.sysenv_var = TR2_SYSENV_PERF,
+};
 
 /*
  * Use TR2_SYSENV_PERF_BRIEF to omit the "<time> <file>:<line>"