mtd: spi-nor: spansion: Rename method to cypress_nor_get_page_size

The method queries SPINOR_REG_CYPRESS_CFR3V to determine the page size.
Rename the method accordingly, s/set/get.

Link: https://lore.kernel.org/r/cd3fb2cbc42a9576377ce4506eec72a58240805d.1680849425.git.Takahiro.Kuwano@infineon.com


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