Count is initially 1 but is assigned to 2 in case PS2_READ_DATA_BYTE.
Though the state machine doesn't go back from PS2_READ_DATA_BYTE to
PS2_READ_BYTE_ONE (not a true bug), force assign Count to 1 to avoid
potential buffer overflow issue.
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Ruiyu Ni <ruiyu.ni@intel.com>
Reviewed-by: Shumin Qiu <shumin.qiu@intel.com>