b43: Fix unaligned 32bit SHM-shared access

This fixes unaligned 32bit SHM-shared read/write access.
The low and high 16 bits were swapped.
It also adds a testcase for this to the chipaccess validation.

(Thanks to Albert Herranz for tracking down this bug.)

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