Qcamera2: remove the unused variable

It could cause some build breakage.

Bug: 21660414
Change-Id: I7bd7cf71e32c48f10131cf978b95dd0d8b3fc451
(cherry picked from commit de9670befab3cb1610a4bab63171714779648ece)
diff --git a/camera/QCamera2/stack/mm-camera-interface/src/mm_camera_interface.c b/camera/QCamera2/stack/mm-camera-interface/src/mm_camera_interface.c
index 8551941..916b6c0 100644
--- a/camera/QCamera2/stack/mm-camera-interface/src/mm_camera_interface.c
+++ b/camera/QCamera2/stack/mm-camera-interface/src/mm_camera_interface.c
@@ -402,7 +402,6 @@
 static int32_t mm_camera_intf_error_close(uint32_t camera_handle)
 {
     int32_t rc = -1;
-    uint8_t cam_idx = camera_handle & 0x00ff;
     mm_camera_obj_t * my_obj = NULL;
 
     CDBG("%s E: camera_handler = %d ", __func__, camera_handle);