tests: setprop_inplace: use xstrdup instead of unchecked strdup

This is the only strdup instance we have, all others are xstrdup. As
strdup is _POSIX_C_SOURCE >= v200809L, which we don't require and we
don't check strdup error return here, switch to xstrdup instead. This
aligns the test with others that call xfuncs, mainly xmalloc().

Signed-off-by: Ahmad Fatoum <a.fatoum@pengutronix.de>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>

tests/setprop_inplace.c

@@ -58,7 +58,7 @@ int main(int argc, char *argv[])
 			     TEST_STRING_1);
 
 	verbose_printf("Old string value was \"%s\"\n", strp);
-	xstr = strdup(strp);
+	xstr = xstrdup(strp);
 	xlen = strlen(xstr);
 	for (i = 0; i < xlen; i++)
 		xstr[i] = toupper(xstr[i]);