[SPARC]: fix sparc64 gcc 4.2 compile failure

[SPARC]: fix sparc64 gcc 4.2 compile failure

Compiling 2.6.21-rc5 with gcc-4.2.0 20070317 (prerelease)
for sparc64 fails as follows:

  gcc -Wp,-MD,arch/sparc64/kernel/.time.o.d  -nostdinc -isystem /home/mikpe/pkgs/linux-sparc64/gcc-4.2.0/lib/gcc/sparc64-unknown-linux-gnu/4.2.0/include -D__KERNEL__ -Iinclude  -include include/linux/autoconf.h -Wall -Wundef -Wstrict-prototypes -Wno-trigraphs -fno-strict-aliasing -fno-common -Os -m64 -pipe -mno-fpu -mcpu=ultrasparc -mcmodel=medlow -ffixed-g4 -ffixed-g5 -fcall-used-g7 -Wno-sign-compare -Wa,--undeclared-regs -fomit-frame-pointer  -fno-stack-protector -Wdeclaration-after-statement -Wno-pointer-sign -Werror   -D"KBUILD_STR(s)=#s" -D"KBUILD_BASENAME=KBUILD_STR(time)"  -D"KBUILD_MODNAME=KBUILD_STR(time)" -c -o arch/sparc64/kernel/time.o arch/sparc64/kernel/time.c
cc1: warnings being treated as errors
arch/sparc64/kernel/time.c: In function 'kick_start_clock':
arch/sparc64/kernel/time.c:559: warning: overflow in implicit constant conversion
make[1]: *** [arch/sparc64/kernel/time.o] Error 1
make: *** [arch/sparc64/kernel] Error 2

gcc gets unhappy when the MSTK_SET macro's u8 __val variable
is updated with &= ~0xff (MSTK_YEAR_MASK). Making the constant
unsigned fixes the problem.

[ I fixed up the sparc32 side as well -DaveM ]

Signed-off-by: Mikael Pettersson <mikpe@it.uu.se>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Adrian Bunk <bunk@kernel.org>