Pointers drop_leaf and save_leaf are initialized with values that are never
read, they are being re-assigned later on just before they are used. Remove
the redundant early initializations and keep the later assignments at the
point where they are used. Cleans up two clang scan build warnings:

fs/xfs/libxfs/xfs_attr_leaf.c:2288:29: warning: Value stored to 'drop_leaf'
during its initialization is never read [deadcode.DeadStores]
fs/xfs/libxfs/xfs_attr_leaf.c:2289:29: warning: Value stored to 'save_leaf'
during its initialization is never read [deadcode.DeadStores]
Signed-off-by: Colin Ian King <colin.i.king@gmail.com>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Signed-off-by: Darrick J. Wong <djwong@kernel.org>