drivers/ipmi: Change type of custom_count from int to size_t
The variable `custom_count` is the number of custom fields, so only
holds non-negative values, so change the struct member type from int to
size_t.
Change-Id: Ic35aafefc870092298523ba2e10adf4fcb687a01
Signed-off-by: Paul Menzel <pmenzel@molgen.mpg.de>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/60790
Reviewed-by: Angel Pons <th3fanbus@gmail.com>
Reviewed-by: Felix Held <felix-coreboot@felixheld.de>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>