oocd_trace: fix warnings

gcc (Gentoo Hardened 4.6.3 p1.13) produces a warning about the variable
assigned but not used. write() can sometimes write less than the specified
count so it's marked with warn_unused_result in the system headers and its
return value can't be ignored. The most correct solution would be to have a
loop writing the buffer until all bytes are written or an error is
returned but here it's impractical.

Change-Id: I75f7482e2b26fe0e6d70d34947518d3a8f0afe5c
Signed-off-by: Paul Fertser <fercerpav@gmail.com>
Reviewed-on: http://openocd.zylin.com/1490
Reviewed-by: Laszlo Papp <lpapp@kde.org>
Tested-by: jenkins
Reviewed-by: Spencer Oliver <spen@spen-soft.co.uk>

src/target/oocd_trace.c

@@ -38,6 +38,8 @@ static int oocd_trace_read_reg(struct oocd_trace *oocd_trace, int reg, uint32_t
 
 	cmd = 0x10 | (reg & 0x7);
 	bytes_written = write(oocd_trace->tty_fd, &cmd, 1);
+	if (bytes_written < 1)
+		return ERROR_FAIL;
 
 	bytes_to_read = 4;
 	while (bytes_to_read > 0) {
@@ -62,6 +64,9 @@ static int oocd_trace_write_reg(struct oocd_trace *oocd_trace, int reg, uint32_t
 	data[4] = (value & 0xff000000) >> 24;
 
 	bytes_written = write(oocd_trace->tty_fd, data, 5);
+	if (bytes_written < 5)
+		return ERROR_FAIL;
+
 	LOG_DEBUG("reg #%i: 0x%8.8x", reg, value);
 
 	return ERROR_OK;
@@ -78,6 +83,8 @@ static int oocd_trace_read_memory(struct oocd_trace *oocd_trace, uint8_t *data,
 
 	cmd = 0x20;
 	bytes_written = write(oocd_trace->tty_fd, &cmd, 1);
+	if (bytes_written < 1)
+		return ERROR_FAIL;
 
 	bytes_to_read = size * 16;
 	while (bytes_to_read > 0) {
@@ -358,6 +365,8 @@ COMMAND_HANDLER(handle_oocd_trace_resync_command)
 	cmd_array[0] = 0xf0;
 
 	bytes_written = write(oocd_trace->tty_fd, cmd_array, 1);
+	if (bytes_written < 1)
+		return ERROR_FAIL;
 
 	command_print(CMD_CTX, "requesting traceclock resync");
 	LOG_DEBUG("resyncing traceclk pll");