sh: rename suffix-y to suffix_y

'export suffix-y' does not work reliably because hyphens are disallowed
in shell variables.

A similar issue was fixed by commit 2bfbe7881ee0 ("kbuild: Do not use
hyphen in exported variable name").

If I do similar in dash, ARCH=sh fails to build.

$ mv linux linux~
$ cd linux~
$ dash
$ make O=foo/bar ARCH=sh CROSS_COMPILE=sh4-linux-gnu- defconfig all
make[1]: Entering directory '/home/masahiro/linux~/foo/bar'
[ snip ]
make[4]: *** No rule to make target 'arch/sh/boot/compressed/vmlinux.bin.', needed by 'arch/sh/boot/compressed/piggy.o'. Stop.
make[3]: *** [/home/masahiro/linux~/arch/sh/boot/Makefile:40: arch/sh/boot/compressed/vmlinux] Error 2
make[2]: *** [/home/masahiro/linux~/arch/sh/Makefile:194: zImage] Error 2
make[1]: *** [/home/masahiro/linux~/Makefile:350: __build_one_by_one] Error 2
make[1]: Leaving directory '/home/masahiro/linux~/foo/bar'
make: *** [Makefile:219: __sub-make] Error 2

The maintainer of GNU Make stated that there is no consistent way to
export variables that do not meet the shell's naming criteria.
(https://savannah.gnu.org/bugs/?55719)

Consequently, you cannot use hyphens in exported variables.

Signed-off-by: Masahiro Yamada <[e-mail]>
Reviewed-by: Nicolas Schier <[e-mail]>

arch/sh/boot/Makefile

···
 CONFIG_ENTRY_OFFSET	?= 0x00001000
 CONFIG_PHYSICAL_START	?= $(CONFIG_MEMORY_START)
 
-suffix-y := bin
-suffix-$(CONFIG_KERNEL_GZIP)	:= gz
-suffix-$(CONFIG_KERNEL_BZIP2)	:= bz2
-suffix-$(CONFIG_KERNEL_LZMA)	:= lzma
-suffix-$(CONFIG_KERNEL_XZ)	:= xz
-suffix-$(CONFIG_KERNEL_LZO)	:= lzo
+suffix_y := bin
+suffix_$(CONFIG_KERNEL_GZIP)	:= gz
+suffix_$(CONFIG_KERNEL_BZIP2)	:= bz2
+suffix_$(CONFIG_KERNEL_LZMA)	:= lzma
+suffix_$(CONFIG_KERNEL_XZ)	:= xz
+suffix_$(CONFIG_KERNEL_LZO)	:= lzo
 
 targets := zImage vmlinux.srec romImage uImage uImage.srec uImage.gz \
 	   uImage.bz2 uImage.lzma uImage.xz uImage.lzo uImage.bin \
···
 $(obj)/uImage.srec: $(obj)/uImage FORCE
 	$(call if_changed,objcopy)
 
-$(obj)/uImage: $(obj)/uImage.$(suffix-y)
+$(obj)/uImage: $(obj)/uImage.$(suffix_y)
 	@ln -sf $(notdir $<) $@
 	@echo '  Image $@ is ready'
 
 export CONFIG_PAGE_OFFSET CONFIG_MEMORY_START CONFIG_BOOT_LINK_OFFSET \
        CONFIG_PHYSICAL_START CONFIG_ZERO_PAGE_OFFSET CONFIG_ENTRY_OFFSET \
-       KERNEL_MEMORY suffix-y
+       KERNEL_MEMORY suffix_y

arch/sh/boot/compressed/Makefile

···
 
 LDFLAGS_piggy.o := -r --format binary --oformat $(ld-bfd) -T
 
-$(obj)/piggy.o: $(obj)/vmlinux.scr $(obj)/vmlinux.bin.$(suffix-y) FORCE
+$(obj)/piggy.o: $(obj)/vmlinux.scr $(obj)/vmlinux.bin.$(suffix_y) FORCE
 	$(call if_changed,ld)