[S] Change in coreboot[master]: libpayload: Fix compiler warnings

[Paul Menzel (Code Review)]

Attention is currently required from: Nico Huber, Thomas Heijligen.

Paul Menzel has posted comments on this change. ( https://review.coreboot.org/c/coreboot/+/69764 )

Change subject: libpayload: Fix compiler warnings
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Patch Set 2:

(2 comments)

Commit Message:

https://review.coreboot.org/c/coreboot/+/69764/comment/b9cc06db_3155f50d 
PS2, Line 8: 
Please mention the compiler.

https://review.coreboot.org/c/coreboot/+/69764/comment/343115dd_fdb5a8f5 
PS2, Line 9: drivers/serial/8250.c:75: [-Werror=unused-variable]
           :   Move variable declaration inside the
           :   `#if !CONFIG(LP_PL011_SERIAL_CONSOLE)` block
           : 
           : drivers/udc/dwc2.c:505: [-Werror=format=]
           :   use `%zd` to match type `size_t`
Next time, it’d be great, if you did two commits with a commit message about the change. “Fix compiler warnings” is too broad in my opinion, and people have to look at the diff to know what it is about.