rtc: silence section mismatch warning in rtc-test

Fix following warning:
WARNING: vmlinux.o(.data+0x253e28): Section mismatch in reference from the variable test_drv to the function .devexit.text:test_remove()

Fix by renaming the platfrom_driver variable from *_drv to *_driver
so modpost ignore the reference to an __devexit section.

Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Cc: Alessandro Zummo <a.zummo@towertech.it>
Cc: David Brownell <david-b@pacbell.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>