Increase length to be copied to be large enough to overcome the
following compilation error. The buf is large enough for this purpose.

drivers/dma/xilinx/xilinx_dpdma.c: In function ‘xilinx_dpdma_debugfs_desc_done_irq_read’:
drivers/dma/xilinx/xilinx_dpdma.c:313:39: error: ‘snprintf’ output may be truncated before the last format character [-Werror=format-truncation=]
  313 |         snprintf(buf, out_str_len, "%d",
      |                                       ^
drivers/dma/xilinx/xilinx_dpdma.c:313:9: note: ‘snprintf’ output between 2 and 6 bytes into a destination of size 5
  313 |         snprintf(buf, out_str_len, "%d",
      |         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  314 |                  dpdma_debugfs.xilinx_dpdma_irq_done_count);
      |                  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Signed-off-by: Vinod Koul <vkoul@kernel.org>
Link: https://lore.kernel.org/r/20231222094017.731917-1-vkoul@kernel.orgSigned-off-by: Vinod Koul <vkoul@kernel.org>