mtd: spi-nor: Fix shift-out-of-bounds in spi_nor_set_erase_type

In the Linux kernel, the following vulnerability has been resolved:

mtd: spi-nor: Fix shift-out-of-bounds in spi_nor_set_erase_type

spi_nor_set_erase_type() was used either to set or to mask out an erase

type. When we used it to mask out an erase type a shift-out-of-bounds

was hit:

UBSAN: shift-out-of-bounds in drivers/mtd/spi-nor/core.c:2237:24

shift exponent 4294967295 is too large for 32-bit type 'int'

The setting of the size_{shift, mask} and of the opcode are unnecessary

when the erase size is zero, as throughout the code just the erase size

is considered to determine whether an erase type is supported or not.

Setting the opcode to 0xFF was wrong too as nobody guarantees that 0xFF

is an unused opcode. Thus when masking out an erase type, just set the

erase size to zero. This will fix the shift-out-of-bounds.

[ta: refine changes, new commit message, fix compilation error]