mtd: spi_nor: fix issue on macronix quad enable bit

Invert test logic on the status register control to
fix issue when the bit SR_QUAD_EN_MX is not set.

Signed-off-by: Lionel Debieve <lionel.debieve@st.com>
Change-Id: I8b2f140219f124336bf96462abf9d9445d0308bc
Reviewed-on: https://gerrit.st.com/c/mpu/oe/st/tf-a/+/185745


Reviewed-by: CITOOLS <smet-aci-reviews@lists.codex.cro.st.com>
Reviewed-by: CIBUILD <smet-aci-builds@lists.codex.cro.st.com>
Reviewed-by: Christophe KERELLO <christophe.kerello@st.com>
Reviewed-by: Yann GAUTIER <yann.gautier@st.com>