wan: wanxl: remove redundant assignment to stat

stat set to zero and the value is never read, instead stat is
set again in the do-loop. Hence the setting to zero is redundant
and can be removed. Cleans up clang warning:

drivers/net/wan/wanxl.c:737:2: warning: Value stored to 'stat'
is never read

Signed-off-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: David S. Miller <davem@davemloft.net>