slcanpty: remove redundant asc2nibble()

asc2nibble() is already defined in lib.h. Include lib.h in slcnpty.c
so that asc2nibble() does not need to be redefined a second time and
adjust the Makefile accordingly.

Signed-off-by: Vincent Mailhol <mailhol.vincent@wanadoo.fr>
Acked-by: Oliver Hartkopp <socketcan@hartkopp.net>
Link: https://lore.kernel.org/all/20221114163848.3398-2-mailhol.vincent@wanadoo.fr
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>

CMakeLists.txt

@@ -33,6 +33,7 @@ set(PROGRAMS_CANLIB
     cansequence
     log2asc
     log2long
+    slcanpty
 )
 
 set(PROGRAMS_J1939
@@ -58,7 +59,6 @@ set(PROGRAMS
     isotptun
     slcan_attach
     slcand
-    slcanpty
 )
 
 add_executable(can-calc-bit-timing