drm/appletbdrm: Fix format specifier for size_t variables

When building for a 32-bit platform, there are some warnings (or errors
with CONFIG_WERROR=y) due to an incorrect specifier for 'size_t'
variables, which is typedef'd as 'unsigned int' for these architectures:

  drivers/gpu/drm/tiny/appletbdrm.c:171:17: error: format specifies type 'unsigned long' but the argument has type 'size_t' (aka 'unsigned int') [-Werror,-Wformat]
    170 |                 drm_err(drm, "Actual size (%d) doesn't match expected size (%lu)\n",
        |                                                                             ~~~
        |                                                                             %zu
    171 |                         actual_size, size);
        |                                      ^~~~
  ...
  drivers/gpu/drm/tiny/appletbdrm.c:212:17: error: format specifies type 'unsigned long' but the argument has type 'size_t' (aka 'unsigned int') [-Werror,-Wformat]
    211 |                 drm_err(drm, "Actual size (%d) doesn't match expected size (%lu)\n",
        |                                                                             ~~~
        |                                                                             %zu
    212 |                         actual_size, size);
        |                                      ^~~~

Use '%zu' as suggested, clearing up the warnings.

Fixes: 0670c2f5 ("drm/tiny: add driver for Apple Touch Bars in x86 Macs")
Signed-off-by: Nathan Chancellor <nathan@kernel.org>
Reviewed-by: Jani Nikula <jani.nikula@intel.com>
Acked-by: Aditya Garg <gargaditya08@live.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20250304-appletbdrm-fix-size_t-specifier-v1-1-94fe1d2c91f8@kernel.org


Signed-off-by: Jani Nikula <jani.nikula@intel.com>