NFSD: Remove redundant assignment to variable host_err

Variable host_err is assigned a value that is never read, it is being
re-assigned a value in every different execution path in the following
switch statement. The assignment is redundant and can be removed.

Cleans up clang-scan warning:
warning: Value stored to 'host_err' is never read [deadcode.DeadStores]

Signed-off-by: Colin Ian King <colin.i.king@gmail.com>
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>