drm mode: fix drmIoctl wrapper

Both drmIoctl and ioctl define second argument as unigned long.

Debugging/tracing tools (like strace or valgrind) on 64-bit machines see
different request value for ioctls with 32nd bit set, because casting
signed int to unsigned long extends 32nd bit to upper word, so 0x80000000
becomes 0xFFFFFFFF80000000)

Nobody noticed because higher 32 bits are chopped off on their way to kernel.