neighbour: Remove redundant initialization of 'bucket'

Integer variable 'bucket' is being initialized however
this value is never read as 'bucket' is assigned zero
in for statement. Remove the redundant assignment.

Cleans up clang warning:

net/core/neighbour.c:3144:6: warning: Value stored to 'bucket' during
its initialization is never read [clang-analyzer-deadcode.DeadStores]

Reported-by: Abaci Robot <abaci@linux.alibaba.com>
Signed-off-by: Yang Li <yang.lee@linux.alibaba.com>
Signed-off-by: David S. Miller <davem@davemloft.net>