drm/imagination: move update_logtype() into ifdef section

drm/imagination: move update_logtype() into ifdef section

This function is only used when debugfs is enabled, and otherwise
causes a build warning:

drivers/gpu/drm/imagination/pvr_fw_trace.c:135:1: error: 'update_logtype' defined but not used [-Werror=unused-function]

Move the #ifdef check to include this function as well.

Fixes: cb56cd610866 ("drm/imagination: Add firmware trace to debugfs")
Acked-by: Frank Binns <frank.binns@imgtec.com>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Link: https://lore.kernel.org/r/20231204073231.1164163-1-arnd@kernel.org
Signed-off-by: Maxime Ripard <mripard@kernel.org>