p54spi: replace internal "cx3110x" name with "p54spi"

While the comment removed in this patch claims board_n800.c uses
"cx3110x", it was never merged to mainline like this.  Mainlined board
files for Nokia N8x0 devices are expected "p54spi", and thus don't
work because the modalias is "cx3110x".  To my knowledge, these
devices are the only real-world use of p54spi, and will not work
without this change.  Tested against my Nokia N810.

Signed-off-by: Luke Dashjr <luke-jr+git@utopios.org>
Signed-off-by: John W. Linville <linville@tuxdriver.com>