ath5k: Remove unused BUG_ON

ath5k: Remove unused BUG_ON

Clang warns that the address of a pointer will always evaluated as true
in a boolean context:

drivers/net/wireless/ath/ath5k/debug.c:1031:14: warning: address of
array 'ah->sbands' will always evaluate to 'true'
[-Wpointer-bool-conversion]
        BUG_ON(!ah->sbands);
               ~~~~~^~~~~~
./include/asm-generic/bug.h:61:45: note: expanded from macro 'BUG_ON'
#define BUG_ON(condition) do { if (unlikely(condition)) BUG(); } while (0)
                                            ^~~~~~~~~
./include/linux/compiler.h:77:42: note: expanded from macro 'unlikely'
# define unlikely(x)    __builtin_expect(!!(x), 0)
                                            ^
1 warning generated.

Given that this condition is always false because of the logical not,
just remove it.

Link: https://github.com/ClangBuiltLinux/linux/issues/130
Signed-off-by: Nathan Chancellor <natechancellor@gmail.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>