tests: benchmarks: peripheral_load: update flash_thread log name

The flash_thread is using a colliding name when registering with
the log module LOG_MODULE_REGISTER(flash, LOG_LEVEL_INF). Update
name to flash_thd to avoid naming collision.

Signed-off-by: Bjarki Arge Andreasen <bjarki.andreasen@nordicsemi.no>

tests/benchmarks/peripheral_load/src/flash_thread.c

@@ -5,7 +5,7 @@
  */
 
 #include <zephyr/logging/log.h>
-LOG_MODULE_REGISTER(flash, LOG_LEVEL_INF);
+LOG_MODULE_REGISTER(flash_thd, LOG_LEVEL_INF);
 
 #include <zephyr/drivers/flash.h>
 #include <zephyr/devicetree.h>