Bluetooth: btmtk: Remove resetting mt7921 before downloading the fw

Remove resetting mt7921 before downloading the fw, as it may cause
command timeout when performing the reset.

Signed-off-by: Hao Qin <hao.qin@mediatek.com>
Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>