drivers: flash: stm32 qspi Enter 4-Byte Address Mode

No need to read back the CR (NOR flash config or control register)
to check if entering the 4-Byte Address Mode is effective.
The action of this command is immediate and the result
(bit field of the CR) is NOR flash vendor-specific.

Signed-off-by: Francois Ramu <francois.ramu@st.com>