wiringpi: fix musl compile

wiringpi: fix musl compile

Fixes [1]:

  wiringPiSPI.c:89:35: error: '_IOC_SIZEBITS' undeclared (first use in this function)

Patch from yocto meta-raspberrypi [2] adding include of asm/ioctl.h.

[1] http://autobuild.buildroot.net/results/e9d/e9d680af7eea6d6c68c8e48248b5cc5b29389baa
[2] https://github.com/agherzan/meta-raspberrypi/blob/master/recipes-devtools/wiringPi/wiringpi/0001-include-asm-ioctl.h-directly-for-_IOC_SIZEBITS.patch

Signed-off-by: Peter Seiderer <ps.report@gmx.net>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>