omap2+: fix build regression

board-generic.c now contains a reference to omap3_timer, but depends
only on ARCH_OMAP2, not on ARCH_OMAP3, which controls that symbol.
omap2_timer seems to be more appropriate anyway, so use that instead.
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Tony Lindgren <tony@atomide.com>

arch/arm/mach-omap2/board-generic.c

@@ -72,5 +72,5 @@ MACHINE_START(OMAP_GENERIC, "Generic OMAP24xx")
 	.init_early	= omap_generic_init_early,
 	.init_irq	= omap2_init_irq,
 	.init_machine	= omap_generic_init,
-	.timer		= &omap3_timer,
+	.timer		= &omap2_timer,
 MACHINE_END