Rename br_flash_id to br_flash_dev_id.

Similarly, it's confusing whether br_flash_id is a flash device ID or
a flash area ID. Make this unambiguous.

Signed-off-by: Marti Bolivar <marti.bolivar@linaro.org>
diff --git a/boot/bootutil/include/bootutil/bootutil.h b/boot/bootutil/include/bootutil/bootutil.h
index 7f76877..c97fc4c 100644
--- a/boot/bootutil/include/bootutil/bootutil.h
+++ b/boot/bootutil/include/bootutil/bootutil.h
@@ -53,7 +53,7 @@
      * The flash offset of the image to execute.  Indicates the position of
      * the image header within its flash device.
      */
-    uint8_t br_flash_id;
+    uint8_t br_flash_dev_id;
     uint32_t br_image_off;
 };
 
diff --git a/boot/bootutil/src/loader.c b/boot/bootutil/src/loader.c
index 74c297c..2b0002f 100644
--- a/boot/bootutil/src/loader.c
+++ b/boot/bootutil/src/loader.c
@@ -1287,7 +1287,7 @@
     }
 
     /* Always boot from the primary slot. */
-    rsp->br_flash_id = boot_img_fa_device_id(&boot_data, 0);
+    rsp->br_flash_dev_id = boot_img_fa_device_id(&boot_data, 0);
     rsp->br_image_off = boot_img_slot_off(&boot_data, 0);
     rsp->br_hdr = boot_img_hdr(&boot_data, slot);
 
diff --git a/boot/bootutil/test/src/boot_test_utils.c b/boot/bootutil/test/src/boot_test_utils.c
index 54fa338..422220b 100644
--- a/boot/bootutil/test/src/boot_test_utils.c
+++ b/boot/bootutil/test/src/boot_test_utils.c
@@ -504,7 +504,7 @@
         }
 
         TEST_ASSERT(memcmp(rsp.br_hdr, slot0hdr, sizeof *slot0hdr) == 0);
-        TEST_ASSERT(rsp.br_flash_id == boot_test_img_addrs[0].flash_id);
+        TEST_ASSERT(rsp.br_flash_dev_id == boot_test_img_addrs[0].flash_id);
         TEST_ASSERT(rsp.br_image_off == boot_test_img_addrs[0].address);
 
         boot_test_util_verify_flash(slot0hdr, orig_slot_0,