fix(drivers/mtd): fix MISRA issues and logic improvement

Fix MISRA issues and invert the spi_nor_ready status
to improve readability.
Remove an unneeded variable initialization.

Change-Id: I25a97fbd6c4389156b4f077b986019fa7c30a457
Signed-off-by: Lionel Debieve <lionel.debieve@st.com>
Signed-off-by: Yann Gautier <yann.gautier@st.com>
1 file changed