drm/edid: for consistency, use mask everywhere for block rev parsing

Other usages of block.rev bitfields were refactored to use FIELD_GET
instead of bitwise ops.

Signed-off-by: Yaroslav Bolyukin <iam@lach.pw>
Reviewed-by: Jani Nikula <jani.nikula@intel.com>

Author: CertainLach

drivers/gpu/drm/drm_displayid_internal.h

@@ -139,6 +139,7 @@ struct displayid_formula_timings_9 {
 	u8 vrefresh;
 } __packed;
 
+#define DISPLAYID_BLOCK_DESCRIPTOR_PAYLOAD_BYTES	GENMASK(6, 4)
 struct displayid_formula_timing_block {
 	struct displayid_block base;
 	struct displayid_formula_timings_9 timings[];

drivers/gpu/drm/drm_edid.c

@@ -6908,7 +6908,8 @@ static int add_displayid_formula_modes(struct drm_connector *connector,
 	struct drm_display_mode *newmode;
 	int num_modes = 0;
 	bool type_10 = block->tag == DATA_BLOCK_2_TYPE_10_FORMULA_TIMING;
-	int timing_size = 6 + ((formula_block->base.rev & 0x70) >> 4);
+	int timing_size = 6 +
+		FIELD_GET(DISPLAYID_BLOCK_DESCRIPTOR_PAYLOAD_BYTES, formula_block->base.rev);
 
 	/* extended blocks are not supported yet */
 	if (timing_size != 6)