spi: intel: Fix the offset to get the 64K erase opcode

According to documentation, the 64K erase opcode is located in VSCC
range [16:23] instead of [8:15].
Use the proper value to shift the mask over the correct range.

Signed-off-by: Mauro Lima <mauro.lima@eclypsium.com>
Reviewed-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Link: https://lore.kernel.org/r/20221012152135.28353-1-mauro.lima@eclypsium.com
Signed-off-by: Mark Brown <broonie@kernel.org>