spi: spidev_test: Use perror() only if errno is not 0

It is better to use perror() only if errno is not 0, it should use printf()
when errno is 0, otherwise there exists redudant ": Success".

E.g. without this patch:

$ ./spidev_test -p 1234 --input test.bin
only one of -p and --input may be selected: Success
Aborted (core dumped)

With this patch:

$ ./spidev_test -p 1234 --input test.bin
only one of -p and --input may be selected
Aborted (core dumped)
Signed-off-by: Tiezhu Yang <yangtiezhu@loongson.cn>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://lore.kernel.org/r/1581567368-8055-3-git-send-email-yangtiezhu@loongson.cnSigned-off-by: Mark Brown <broonie@kernel.org>

tools/spi/spidev_test.c

@@ -13,6 +13,7 @@
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
+#include <errno.h>
 #include <getopt.h>
 #include <fcntl.h>
 #include <time.h>
@@ -26,7 +27,11 @@
 
 static void pabort(const char *s)
 {
-	perror(s);
+	if (errno != 0)
+		perror(s);
+	else
+		printf("%s\n", s);
+
 	abort();
 }