[spi_device] Lint Fix

Revise the ARITH_BITLEN mismatch and LHS_SHORT errors.

Signed-off-by: Eunchan Kim <eunchan@opentitan.org>

hw/ip/spi_device/rtl/spid_upload.sv

diff --git a/hw/ip/spi_device/rtl/spid_upload.sv b/hw/ip/spi_device/rtl/spid_upload.sv
index a83ce67..b03fabb 100644
--- a/hw/ip/spi_device/rtl/spid_upload.sv
+++ b/hw/ip/spi_device/rtl/spid_upload.sv
@@ -282,7 +282,7 @@
         // payloadptr reached max
         payload_max <= 1'b 1;
       end
-      payloadptr <= payloadptr + PayloadPtrW'(1);
+      payloadptr <= payloadptr + PayloadIdxW'(1);
     end
   end