stm32: Correct positioning of declaration

stm32: Correct positioning of declaration

The current code gives a warning:

arch/arm/mach-stm32/stm32f7/soc.c: In function 'arch_cpu_init':
arch/arm/mach-stm32/stm32f7/soc.c:38:2: error: 'for' loop initial
    declarations are only allowed in C99 or C11 mode
  for (int i = 0; i < ARRAY_SIZE(stm32_region_config); i++)
  ^
arch/arm/mach-stm32/stm32f7/soc.c:38:2: note: use option -std=c99,
    -std=gnu99, -std=c11 or -std=gnu11 to compile your code

Fix it by moving the declaration to the top of the function.

Signed-off-by: Simon Glass <sjg@chromium.org>
Series-cc trini