mtd: spi-nor: spansion: switch s25hx_t to use vreg_offset for quad_enable()

All s25hx_t flashes have single or multi chip flavors and already use
n_dice and vreg_offset in cypress_nor_sr_ready_and_clear. Switch s25hx_t
to always use vreg_offset for the quad_enable() method, so that we use
the same code base for both single and multi chip package flashes.

Tested-by: Takahiro Kuwano <Takahiro.Kuwano@infineon.com>
Link: https://lore.kernel.org/r/20230726075257.12985-11-tudor.ambarus@linaro.org
Signed-off-by: Tudor Ambarus <tudor.ambarus@linaro.org>