drm/i915/display: Fix an unsigned subtraction which can never be negative.

smatch warning:
drivers/gpu/drm/i915/display/intel_dmc.c:601 parse_dmc_fw() warn:
unsigned 'fw->size - offset' is never less than zero

Firmware size is size_t and offset is u32. So the subtraction is
unsigned which can never be less than zero.

Fixes: 3d5928a ("drm/i915/xelpd: Pipe A DMC plugging")
Signed-off-by: Harshit Mogalapalli <[email protected]>
Reviewed-by: Lucas De Marchi <[email protected]>
Signed-off-by: Lucas De Marchi <[email protected]>
Link: https://patchwork.freedesktop.org/patch/msgid/[email protected]
(cherry picked from commit 87bb2a4)
Signed-off-by: Rodrigo Vivi <[email protected]>

Author: harshimogalapalli

drivers/gpu/drm/i915/display/intel_dmc.c

@@ -596,7 +596,7 @@ static void parse_dmc_fw(struct drm_i915_private *dev_priv,
 			continue;
 
 		offset = readcount + dmc->dmc_info[id].dmc_offset * 4;
-		if (fw->size - offset < 0) {
+		if (offset > fw->size) {
 			drm_err(&dev_priv->drm, "Reading beyond the fw_size\n");
 			continue;
 		}