libpayload: hexdump.c: Change type of length argument to size_t

Representing a (non-negative) length with a signed integer is not
optimal, so change its type to `size_t`.

Change-Id: Ic0c2b7e081ba32d917409568ee53007d9ab7f8f3
Signed-off-by: Paul Menzel <paulepanter@users.sourceforge.net>
Reviewed-on: http://review.coreboot.org/4768
Tested-by: build bot (Jenkins)
Reviewed-by: Patrick Georgi <patrick@georgi-clan.de>
2 files changed