clocksource: fixup ux500 build problems

Based on a patch from Arnd Bergmann this fixes up the build
problem of assigning a non-existing global when the ux500 PRCMU
timer is not linked in by passing its base address to the init
function. We also add a missing <linux/errno.h> inclusion and
staticize the dummy function.

Cc: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
diff --git a/include/linux/clksrc-dbx500-prcmu.h b/include/linux/clksrc-dbx500-prcmu.h
index d1e9504..4fb8119 100644
--- a/include/linux/clksrc-dbx500-prcmu.h
+++ b/include/linux/clksrc-dbx500-prcmu.h
@@ -11,12 +11,10 @@
 #include <linux/init.h>
 #include <linux/io.h>
 
-extern void __iomem *clksrc_dbx500_timer_base;
-
 #ifdef CONFIG_CLKSRC_DBX500_PRCMU
-void __init clksrc_dbx500_prcmu_init(void);
+void __init clksrc_dbx500_prcmu_init(void __iomem *base);
 #else
-void __init clksrc_dbx500_prcmu_init(void) {}
+static inline void __init clksrc_dbx500_prcmu_init(void __iomem *base) {}
 #endif
 
 #endif