b43: use temporary rate_index for error checking
b43: use temporary rate_index for error checking

The mac80211 rate_index changed to be a u8, so
can't hold the negative error value properly.
Use a temporary variable for error checking.

Reported-by: Dan Carpenter <ff341aa343d564f9e53e9dcb6996be8c04859a66@oracle.com>
Signed-off-by: Johannes Berg <bff32994ff0f8d048f262a8388145a71b6071bfe@intel.com>
Signed-off-by: John W. Linville <2a53bac7a5d324865ef46ec4c38b2c0fba1456b4@tuxdriver.com>

KristFoundation/Programs,KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs