mtd: spi-nor: sfdp: Fix wrong erase type bitmask for overlaid region

At the time spi_nor_region_check_overlay() is called, the erase types are
sorted in ascending order of erase size. The 'erase_type' should be masked
with 'BIT(erase[i].idx)' instead of 'BIT(i)'.

Fixes: b038e8e3 ("mtd: spi-nor: parse SFDP Sector Map Parameter Table")
Cc: stable@vger.kernel.org
Signed-off-by: Takahiro Kuwano <Takahiro.Kuwano@infineon.com>
[ta: Add Fixes tag and Cc to stable]
Signed-off-by: Tudor Ambarus <tudor.ambarus@microchip.com>
Link: https://lore.kernel.org/r/fd90c40d5b626a1319a78fc2bcee79a8871d4d57.1601612872.git.Takahiro.Kuwano@infineon.com