spi: uapi: spidev: add missing ioctl header

The SPI_IOC_MESSAGE() macro references _IOC_SIZEBITS. Add linux/ioctl.h
to make sure this macro is defined. This fixes the following build
failure of lcdproc with the musl libc:

In file included from .../sysroot/usr/include/sys/ioctl.h:7:0,
                 from hd44780-spi.c:31:
hd44780-spi.c: In function 'spi_transfer':
hd44780-spi.c:89:24: error: '_IOC_SIZEBITS' undeclared (first use in this function)
  status = ioctl(p->fd, SPI_IOC_MESSAGE(1), &xfer);
                        ^

Signed-off-by: Baruch Siach <baruch@tkos.co.il>
Signed-off-by: Mark Brown <broonie@kernel.org>
Cc: stable@vger.kernel.org