checkpatch: Ignore 'short' Kconfig help entries

A 2 line help entry for a new Kconfig entry is, at this time, sufficient
in some cases, so lets drop that warning for now.

Signed-off-by: Tom Rini <trini@konsulko.com>

.checkpatch.conf

@@ -25,3 +25,6 @@
 # Ignore "WARNING: Prefer ether_addr_copy() over memcpy() if the Ethernet
 # addresses are __aligned(2)".
 --ignore PREFER_ETHER_ADDR_COPY
+
+# A bit shorter of a description is OK with us.
+--min-conf-desc-length=2