e1000e: fix double release of mutex

During a reset, releasing the swflag after it failed to be acquired would
cause a double unlock of the mutex.  Instead, test whether acquisition of
the swflag was successful and if not, do not release the swflag.  The reset
must still be done to bring the device to a quiescent state.

This resolves [BUG 12200] BUG: bad unlock balance detected! e1000e
http://bugzilla.kernel.org/show_bug.cgi?id=12200

Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>