sparc64: fix sparse warning in traps_64.c

Fix following warning:
traps_64.c:2384:6: error: symbol 'die_if_kernel' redeclared with different type (originally declared at include/asm/bug.h:23) - different modifiers

Add proper __noreturn to the implementation to fix this

Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Signed-off-by: David S. Miller <davem@davemloft.net>