How about this function, which combines biomaRt and AnnotationHub to get the results.  

library(AnnotationHub)
library(GenomicRanges)
library(biomaRt)
library(dplyr)

snp2cyto <- function(snp_ids) {
  
  ## query ensembl snp mart to find coordinates for each SNP
  snpmart <- useMart("ENSEMBL_MART_SNP", dataset = "hsapiens_snp")
  snp_locs <- getBM(attributes = c('refsnp_id', "chr_name", 
                                   "chrom_start", "chrom_end"), 
                    filters = 'snp_filter',
                    values = snps,
                    mart = snpmart)
  
  ## load annotation hub and select hg38 genome cytobands
  ah <- AnnotationHub()
  cyto_hg38 <- query(ah, 'AHCytoBands')[['AH53178']]
  
  ## add "chr" to names, and create GRanges for all SNPs
  snp_chrom <- paste0('chr', snp_locs[,2])
  snp_granges <- GRanges(seqnames = snp_chrom, 
                         ranges = IRanges(start = snp_locs[,3], 
                                          end = snp_locs[,4]))
  
  ## match SNPs to cyto bands
  hits <- cyto_hg38[findOverlaps(query = snp_granges, 
                            subject = cyto_hg38, 
                            select = "first")]
  
  ## return values
  data_frame(snp_id = snp_locs[,1],
             chrom = snp_chrom,
             cyto_band = mcols(hits)$name)
  
}

Then if we try the same set of SNPs as before:

snps <-  c('rs905327004', 'rs945943648', 'rs765779967')
snp2cyto(snps)

# A tibble: 3 x 3
       snp_id chrom cyto_band
        <chr> <chr>    <fctr>
1 rs765779967 chr16       q21
2 rs905327004  chr1    p36.33
3 rs945943648  chr8     p23.1

I'm sure there's an AnnotationHub only way of doing it, but that seems to get where I think you need to be.