xfsprogs: remove unreachable code in libxfs_inode_alloc

xfsprogs: remove unreachable code in libxfs_inode_alloc

This code does:

        if (!ialloc_context && !ip)
                return;

        // if !ip here, ialloc_context must be true

        if (ialloc_context) {
                ...
                if (!ip)
                        error = ENOSPC;
                if (error)
                        return error;
                // if !ip in this block we've returned
        }

        // so (!ip) cannot be true here
        if (!ip)
                error = ENOSPC;

(cherry picked this one out of Coverity reports)

Signed-off-by: Eric Sandeen <sandeen@redhat.com>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Dave Chinner <david@fromorbit.com>