spi: stm32-qspi: fix debug format string

Printing size_t needs a special %zx format modifier to avoid a
warning like:

drivers/spi/spi-stm32-qspi.c:481:41: note: format string is defined here
  481 |         dev_dbg(qspi->dev, "%s len = 0x%x offs = 0x%llx buf = 0x%p\n", __func__, len, offs, buf);

Patrice already tried to fix this, but picked %lx instead of %zx,
which fixed some architectures but broke others in the same way.
Using %zx works everywhere.

Fixes: 18674dee ("spi: stm32-qspi: Add dirmap support")
Fixes: 1b8a7d42

 ("spi: stm32-qspi: Fix compilation warning in ARM64")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Link: https://lore.kernel.org/r/20210422134955.1988316-1-arnd@kernel.org
Signed-off-by: Mark Brown <broonie@kernel.org>