sc520: fix build warning about unused temp var

Building the eNET_SRAM board fails for me:
	sc520_timer.c: In function 'sc520_udelay':
	sc520_timer.c:81:7: error: variable 'temp' set but not used
		[-Werror=unused-but-set-variable]
	cc1: all warnings being treated as errors
	make[1]: *** [sc520_timer.o] Error 1

Signed-off-by: Mike Frysinger <vapier@gentoo.org>