tg3: Remove unnecessary lock around tg3_flag_set

The spinlock was needed when flags used to be a u32 and set/cleared
using bit operations. Now that we use the atomic set_bit, this lock
isn't needed.

Signed-off-by: Nithin Nayak Sujir <nsujir@broadcom.com>
Signed-off-by: Michael Chan <mchan@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>