rt2x00: Fix pointer errors.

Fix some pointer errors in the various calls to memcpy, memset and memmove.

Although none of these errors are fatal (the expression used now results in
the same pointer value) it is better to use the proper expression.
All errors are having to deal with arrays.

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