stm32mp1: spl: Fix compilation warnings

Fix the following compilation warnings :

../arch/arm/mach-stm32mp/stm32mp1/spl.c: In function 'stm32_init_tzc_for_optee':
../arch/arm/mach-stm32mp/stm32mp1/spl.c:148:37: warning: 'optee_size' may be used uninitialized [-Wmaybe-uninitialized]
  148 |         tee_shmem_base = optee_base + optee_size - CFG_SHMEM_SIZE;
      |                          ~~~~~~~~~~~^~~~~~~~~~~~
../arch/arm/mach-stm32mp/stm32mp1/spl.c:137:30: note: 'optee_size' was declared here
  137 |         uint32_t optee_base, optee_size, tee_shmem_base;
      |                              ^~~~~~~~~~
../arch/arm/mach-stm32mp/stm32mp1/spl.c:148:37: warning: 'optee_base' may be used
uninitialized [-Wmaybe-uninitialized]
  148 |         tee_shmem_base = optee_base + optee_size - CFG_SHMEM_SIZE;
      |                          ~~~~~~~~~~~^~~~~~~~~~~~
../arch/arm/mach-stm32mp/stm32mp1/spl.c:137:18: note: 'optee_base' was declared here
  137 |         uint32_t optee_base, optee_size, tee_shmem_base;
      |                  ^~~~~~~~~~

Fix also the following checkpatch "check" :

CHECK: Prefer kernel type 'u32' over 'uint32_t'
37: FILE: arch/arm/mach-stm32mp/stm32mp1/spl.c:137:
+	uint32_t optee_base = 0, optee_size = 0, tee_shmem_base;

Signed-off-by: Patrice Chotard <patrice.chotard@foss.st.com>
Reviewed-by: Patrick Delaunay <patrick.delaunay@foss.st.com>