b43legacy: Remove switch statement with 64-bit index

The gcc 3.4 fork used to compile the MN10300 port emits unwanted
__ucmpdi2() calls for switch statements that use a 64bit value.

This patch removes such a switch from b43legacy, and makes the code
more like that used in b43. Thanks to Adrian Bunk <bunk@kernel.org>
for reporting the problem.

Signed-off-by: Larry Finger <Larry.Finger@lwfinger.net>
Signed-off-by: John W. Linville <linville@tuxdriver.com>