Staging: brcm80211: remove broken MIN() implementation

Use the kernel-provided version, this one is broken.

Note, there are more compiler warnings now, that's due to different
types being compared, which shows how the original macro was wrong in at
least one way.  They need to be fixed up.

Cc: Brett Rudley <brudley@broadcom.com>
Cc: Henry Ptasinski <henryp@broadcom.com>
Cc: Nohee Ko <noheek@broadcom.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>