__uClibc_main.c: save ~70 bytes by not checking that /dev/null

__uClibc_main.c: save ~70 bytes by not checking that /dev/null
is indeed a char device with correct (maj,min).
(If it's not such a char device, the system is screwed anyway,
nothing can be done about it...)

    text           data     bss     dec     hex filename
-    715              4      21     740     2e4 libc/misc/internals/__uClibc_main.o
+    644              4      21     669     29d libc/misc/internals/__uClibc_main.o