Change in coreboot[master]: drivers/spi: Stop using a variable-length array

[Angel Pons (Code Review)]

Attention is currently required from: Julius Werner, Jacob Garber.
Angel Pons has posted comments on this change. ( https://review.coreboot.org/c/coreboot/+/50480 )

Change subject: drivers/spi: Stop using a variable-length array
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Patch Set 1:

(1 comment)

File src/drivers/spi/spi_flash.c:

https://review.coreboot.org/c/coreboot/+/50480/comment/85b59368_514e7bb6 
PS1, Line 95: 	u8 buff[4 + (1 << DEFAULT_PAGE_SIZE_SHIFT)];
> Hmmm... The problem is that we need to concatenate two buffers. […]

I made CB:50519 to avoid having to concatenate buffers inside this function. I'm not sure if it's an improvement, though.