LOCK key read
RD LCKR[16] = 1 (this read operation is optional but it confirms that the lock is active)
Note: During the LOCK key write sequence, the value of LCK3 must not change.
Note: Any error in the lock sequence aborts the LOCK.
Note: After the first LOCK sequence on any bit of the port, any read access on the LCKK bit returns 1 until the next MCU reset or peripheral reset.
0 (B_0x0): Port configuration lock key not active
1 (B_0x1): Port configuration lock key active. The GPIOH_LCKR register is locked until the next MCU reset or peripheral reset.