docs/renesas-ra: Correct the internal file system size of EK-RA6M2.

Signed-off-by: Takeo Takahashi <[email protected]>

Author: TakeoTakahashi2020

Diff for: docs/renesas-ra/tutorial/program_in_flash.rst

@@ -19,7 +19,7 @@ As the factory setting, following size is allocated for the file system:
  EK-RA4M1           36KB ( 36864B)
  EK-RA4W1           64KB ( 65536B)
  EK-RA6M1          128KB (131072B)
- EK-RA6M2          256KB (262144B)
+ EK-RA6M2          128KB (131072B)
  RA4M1 CLICKER      36KB ( 36864B)
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