p54spi: add "spi:" prefix for stlc45xx modalias

Since commit e0626e38 (spi: prefix modalias with "spi:"),
the spi modalias is prefixed with "spi:".

This patch adds "spi:" prefix for modalias of stlc45xx.
Also move it to be group with other modalias.

Signed-off-by: Axel Lin <axel.lin@gmail.com>
Acked-By: Christian Lamparter <chunkeey@googlemail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>