m68k: add private libgcc ashrdi3

Add ashrdi3.c to private libgcc.

Signed-off-by: Angelo Dureghello <angelo@kernel-space.org>
diff --git a/arch/m68k/lib/Makefile b/arch/m68k/lib/Makefile
index b66d66a..6e1fd93 100644
--- a/arch/m68k/lib/Makefile
+++ b/arch/m68k/lib/Makefile
@@ -5,7 +5,7 @@
 
 ## Build a couple of necessary functions into a private libgcc
 ## if the user asked for it
-lib-$(CONFIG_USE_PRIVATE_LIBGCC) += lshrdi3.o muldi3.o ashldi3.o
+lib-$(CONFIG_USE_PRIVATE_LIBGCC) += lshrdi3.o muldi3.o ashldi3.o ashrdi3.o
 
 obj-y	+= bdinfo.o
 obj-$(CONFIG_CMD_BOOTM) += bootm.o