b43: replace limit_value macro with clamp_val

kernel-provided clamp_val is identical, delete the private limit_value helper.

Signed-off-by: Harvey Harrison <harvey.harrison@gmail.com>
Cc: Michael Buesch <mb@bu3sch.de>
Cc: "John W. Linville" <linville@tuxdriver.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: John W. Linville <linville@tuxdriver.com>