package/flashrom: fix build failures with musl

flashroms makes a few assumptions on the headers to be included.
It forgets that not everything is using glibc, so it is missing
crucial includes.

Fixes:
    http://autobuild.buildroot.org/results/2a3/2a3744007c630c267575a638ebcd83a4b97644f5/
    http://autobuild.buildroot.org/results/3de/3de936d9be79e151e66af15193084d82a0f2c04a/



Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Cc: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>