drivers: flash: ospi driver erase command on 24bits in SPI mode

When configuring the octo-flash in SPI/STR mode, the address size
must be on 24bits (and not on 32bits).
Despite the dev_data->address_width which is always seen as 4, the
erase command must reduce the AddressSize for this transfer mode.

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