can-utils: fix missing include of libgen.h

The basename() function needs libgen.h to be included as otherwise this
will fail to compile in some environments.

Reported-by: Robert Schwebel <r.schwebel@pengutronix.de>
Signed-off-by: Oliver Hartkopp <socketcan@hartkopp.net>

can-calc-bit-timing.c

@@ -23,6 +23,7 @@
 #include <stdint.h>
 #include <stdio.h>
 #include <stdlib.h>
+#include <libgen.h>
 #include <string.h>
 
 #include <linux/types.h>

slcanpty.c

@@ -26,6 +26,7 @@
 
 #include <stdio.h>
 #include <stdlib.h>
+#include <libgen.h>
 #include <string.h>
 #include <unistd.h>
 #include <fcntl.h>