mtd: st_spi_fsm: correct type issues

mtd: st_spi_fsm: correct type issues

Compile-testing for a 64-bit arch uncovers several bad casts:

    In file included from include/linux/linkage.h:4:0,
                     from include/linux/kernel.h:6,
                     from drivers/mtd/devices/st_spi_fsm.c:15:
    drivers/mtd/devices/st_spi_fsm.c: In function ‘stfsm_read_fifo’:
    drivers/mtd/devices/st_spi_fsm.c:758:11: warning: cast from pointer to integer of different size [-Wpointer-to-int-cast]
      BUG_ON((((uint32_t)buf) & 0x3) || (size & 0x3));
    ...

Use uintptr_t instead of uint32_t, since it's guaranteed to be
pointer-sized.

We also see this warning, if size_t is not 32 bits wide:

    In file included from drivers/mtd/devices/st_spi_fsm.c:15:0:
    drivers/mtd/devices/st_spi_fsm.c: In function ‘stfsm_mtd_write’:
    include/linux/kernel.h:712:17: warning: comparison of distinct pointer types lacks a cast [enabled by default]
      (void) (&_min1 == &_min2);  \
                     ^
    drivers/mtd/devices/st_spi_fsm.c:1704:11: note: in expansion of macro ‘min’
       bytes = min(FLASH_PAGESIZE - page_offs, len);
               ^

Just use min_t() to force the type conversion, since we don't really
want to upgrade 'page_offs' and 'bytes' to size_t; they only should be
handling <= 256 byte offsets.

Signed-off-by: Brian Norris <computersforpeace@gmail.com>
Acked-by: Lee Jones <lee.jones@linaro.org>