doc: flash: Fix typo

the off argument of flash_area_write is used to *write*

Signed-off-by: Nicolas VINCENT <nicolas.vincent@vossloh.com>
diff --git a/include/zephyr/storage/flash_map.h b/include/zephyr/storage/flash_map.h
index e07305c..ba82fe5 100644
--- a/include/zephyr/storage/flash_map.h
+++ b/include/zephyr/storage/flash_map.h
@@ -156,7 +156,7 @@
  * as wrapped flash driver.
  *
  * @param[in]  fa  Flash area
- * @param[in]  off Offset relative from beginning of flash area to read
+ * @param[in]  off Offset relative from beginning of flash area to write
  * @param[out] src Buffer with data to be written
  * @param[in]  len Number of bytes to write
  *