spi/gpio: fix section mismatch warning

Fixes:
The function __devinit spi_gpio_probe() references
a function __init spi_gpio_alloc.isra.4().
If spi_gpio_alloc.isra.4 is only used by spi_gpio_probe then
annotate spi_gpio_alloc.isra.4 with a matching annotation.

[wsa: fix spi_gpio_request(), too]

Signed-off-by: Manuel Lauss <manuel.lauss@googlemail.com>
Signed-off-by: Wolfram Sang <w.sang@pengutronix.de>