fpga: altera-pr-ip: fix unsigned comparison with less than zero

Fix the "comparison with less than zero" warning reported by
cppcheck for the unsigned (size_t) parameter count of the
alt_pr_fpga_write() function.

Fixes: d201cc17 ("fpga pr ip: Core driver support for Altera Partial Reconfiguration IP")
Reviewed-by: Tom Rix <trix@redhat.com>
Acked-by: Xu Yilun <yilun.xu@intel.com>
Signed-off-by: Marco Pagani <marpagan@redhat.com>
Link: https://lore.kernel.org/r/20220609140520.42662-1-marpagan@redhat.com


Signed-off-by: Xu Yilun <yilun.xu@intel.com>