mtd: spi-nor: spansion: Enable JFFS2 write buffer for Infineon s25hx SEMPER flash

Infineon(Cypress) SEMPER NOR flash family has on-die ECC and its program
granularity is 16-byte ECC data unit size. JFFS2 supports write buffer
mode for ECC'd NOR flash. Provide a way to clear the MTD_BIT_WRITEABLE
flag in order to enable JFFS2 write buffer mode support.

Fixes: b6b23833 ("mtd: spi-nor: spansion: Add s25hl-t/s25hs-t IDs and fixups")
Suggested-by: Tudor Ambarus <tudor.ambarus@linaro.org>
Signed-off-by: Takahiro Kuwano <Takahiro.Kuwano@infineon.com>
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/r/a1cc128e094db4ec141f85bd380127598dfef17e.1680760742.git.Takahiro.Kuwano@infineon.com


Signed-off-by: Tudor Ambarus <tudor.ambarus@linaro.org>