mmc: Use EXT_CSD_EXTRACT_BOOT_PART() macro for extracting boot part

Mask macro PART_ACCESS_MASK filter out access bits of emmc register and
macro EXT_CSD_EXTRACT_BOOT_PART() extracts boot part bits of emmc register.
So use EXT_CSD_EXTRACT_BOOT_PART() when extracting boot partition.

Signed-off-by: Pali Rohár <pali@kernel.org>
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/common/spl/spl_mmc.c b/common/spl/spl_mmc.c
index bd5e6ad..a072216 100644
--- a/common/spl/spl_mmc.c
+++ b/common/spl/spl_mmc.c
@@ -378,7 +378,7 @@
 	 * 1 and 2 match up to boot0 / boot1 and 7 is user data
 	 * which is the first physical partition (0).
 	 */
-	part = (mmc->part_config >> 3) & PART_ACCESS_MASK;
+	part = EXT_CSD_EXTRACT_BOOT_PART(mmc->part_config);
 	if (part == 7)
 		part = 0;
 #endif