omap3: Fix booting if package is uninitialized

Otherwise bringing up new boards can be harder:

Unable to handle kernel NULL pointer dereference at virtual address 00000000
pgd = c0004000
[00000000] *pgd=00000000
Internal error: Oops: 5 [#1]
last sysfs file:
Modules linked in:
CPU: 0    Not tainted  (2.6.33-rc2-00015-g0bc9c93-dirty #37)
PC is at omap_mux_init+0xa4/0x3d8
LR is at omap_mux_init+0x3c/0x3d8
...
Signed-off-by: Tony Lindgren <tony@atomide.com>

arch/arm/mach-omap2/mux.c

@@ -994,8 +994,10 @@ int __init omap_mux_init(u32 mux_pbase, u32 mux_size,
 	}
 
 #ifdef CONFIG_OMAP_MUX
-	omap_mux_package_fixup(package_subset, superset);
-	omap_mux_package_init_balls(package_balls, superset);
+	if (package_subset)
+		omap_mux_package_fixup(package_subset, superset);
+	if (package_balls)
+		omap_mux_package_init_balls(package_balls, superset);
 	omap_mux_set_cmdline_signals();
 	omap_mux_set_board_signals(board_mux);
 #endif