imx: Fix rounding values

The commit message mentions 8-pixels alignment, whereas rounding is performed to 2^8.
For the width, the rounding factor is 8-pixels, according to the data sheet.
This indicates that the author misunderstood the round_up() semantics in the neighboring roundings too.
2 jobs for formats2 in 65 minutes and 57 seconds (queued for 1 second)
Status Job ID Name Coverage
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passed #367524
librem5
build:aarch64

00:15:04

passed #367525
librem5:arm64
build:deb

01:05:57