drivers: disk: loopback: Remove unnecessary include

This file does not seem to need unistd.h, and that header is a
POSIX extension to the C library which is not avaiable in general.
So let's not include it.

Without this change this file fails to build with minimal libc or
other C libraries which do not have this extra header.

Signed-off-by: Alberto Escolar Piedras <alberto.escolar.piedras@nordicsemi.no>
1 file changed