libbb: add skip_dev_pfx()

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
diff --git a/libbb/skip_whitespace.c b/libbb/skip_whitespace.c
index 7b12326..f5a61a3 100644
--- a/libbb/skip_whitespace.c
+++ b/libbb/skip_whitespace.c
@@ -30,3 +30,10 @@
 
 	return (char *) s;
 }
+
+char* FAST_FUNC skip_dev_pfx(const char *tty_name)
+{
+	if (strncmp(tty_name, "/dev/", 5) == 0)
+		tty_name += 5;
+	return (char*)tty_name;
+}