rt2x00: correct sparse warning in rt2x00debug.c

  CHECK   drivers/net/wireless/rt2x00/rt2x00debug.c
drivers/net/wireless/rt2x00/rt2x00debug.c:193:28: warning: incorrect type in assignment (different base types)
drivers/net/wireless/rt2x00/rt2x00debug.c:193:28:    expected restricted __le32 [usertype] chip_rev
drivers/net/wireless/rt2x00/rt2x00debug.c:193:28:    got restricted __le16 [usertype] <noident>

Signed-off-by: John W. Linville <linville@tuxdriver.com>
Acked-by: Ivo van Doorn <IvDoorn@gmail.com>