mtd: spi-nor: stm32-quadspi: fix compiler errors with COMPILE_TEST

This patch fixes some compiler errors:
- change format strings to use %zx for size_t
- add missing #include <linux/sizes.h>

Cc: Ludovic Barre <ludovic.barre@st.com>
Signed-off-by: Cyrille Pitchen <cyrille.pitchen@wedev4u.fr>