b43: Don't use memcpy for overlapping areas

It is valid to pass &gphy->rfatt and &gphy->bbatt as rfatt and bbatt
pointer arguments to the function. So we have to use memmove for the
possibly overlapping memory areas.

Signed-off-by: Michael Buesch <mb@bu3sch.de>
Signed-off-by: John W. Linville <linville@tuxdriver.com>