h8300/boot: Use POSIX "$((..))" instead of bashism "$[...]"

On Ubuntu, where /bin/sh -> dash, "make ARCH=h8300 clean" gives:

printf: 1: $[0x00400000+0x00140000]: expected numeric value

Replace the bash-specific "$[...]" by POSIX "$((..))" for arithmetic
expansion to fix this.
Note that according to the bash 4.1 manpage, "$[...]" is deprecated, and
will be removed in upcoming versions of bash.
Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>

arch/h8300/boot/compressed/Makefile

@@ -16,7 +16,7 @@ OBJECTS = $(obj)/head.o $(obj)/misc.o
 #
 CONFIG_MEMORY_START     ?= 0x00400000
 CONFIG_BOOT_LINK_OFFSET ?= 0x00140000
-IMAGE_OFFSET := $(shell printf "0x%08x" $$[$(CONFIG_MEMORY_START)+$(CONFIG_BOOT_LINK_OFFSET)])
+IMAGE_OFFSET := $(shell printf "0x%08x" $$(($(CONFIG_MEMORY_START)+$(CONFIG_BOOT_LINK_OFFSET))))
 
 LDFLAGS_vmlinux := -Ttext $(IMAGE_OFFSET) -estartup $(obj)/vmlinux.lds