WAN: dscc4: Fix warning pointing out a bug.

Noticed by Stephen Rothwell:

	Today's linux-next build (x86_64 allmodconfig gcc-4.4.0)
	produced this warning:

	drivers/net/wan/dscc4.c: In function 'dscc4_rx_skb':
	drivers/net/wan/dscc4.c:670: warning: suggest parentheses around comparison in operand of '|'

	which actually points out a bug, I think.  It is doing
		(x & (y | z)) != y | z
	when it probably means
		(x & (y | z)) != (y | z)

	Introduced by commit 5de3fcab


	("WAN: bit and/or confusion").

Signed-off-by: David S. Miller <davem@davemloft.net>