xfs: Remove redundant assignment to busy

Variable busy is set to false, but this value is never read as it is
overwritten or not used later on, hence it is a redundant assignment
and can be removed.

Clean up the following clang-analyzer warning:

fs/xfs/libxfs/xfs_alloc.c:1679:2: warning: Value stored to 'busy' is
never read [clang-analyzer-deadcode.DeadStores].

Reported-by: Abaci Robot <abaci@linux.alibaba.com>
Signed-off-by: Jiapeng Chong <jiapeng.chong@linux.alibaba.com>
Reviewed-by: Brian Foster <bfoster@redhat.com>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Signed-off-by: Darrick J. Wong <djwong@kernel.org>