nios2: add asm-nios2/errno.h

Just pull in asm-generic.

Signed-off-by: Thomas Chou <thomas@wytron.com.tw>
Signed-off-by: Scott McNutt <smcnutt@psyent.com>

include/asm-nios2/errno.h

@@ -0,0 +1 @@
+#include <asm-generic/errno.h>