fix(IconItem.qml): Remove qml M126 warning

fix(IconItem.qml): Remove qml M126 warning

Message:
== and != may perform type coercion, use === or !== to avoid it.

Description:
The non-strict equality comparison is allowed to convert its arguments
to a common type. That can lead to unexpected results such as
' \t\r\n' == 0 being true. Use the strict equality operators === and
!== and be explicit about conversions you require.

Bug-AGL: SPEC-2814

Change-Id: I96de9ecace7ea519946c0df739db9753d44d2dfd
Signed-off-by: Li Xiaoming <lixm.fnst@cn.fujitsu.com>