sparc: fix sparse warnings in arch/sparc/prom for 32 bit build

Fix following sparse warnings:
arch/sparc/prom/bootstr_32.c:32:35: warning: Using plain integer as NULL pointer
arch/sparc/prom/memory.c:61:13: warning: symbol 'prom_meminit' was not declared. Should it be static?
arch/sparc/prom/misc_32.c:74:1: error: symbol 'prom_halt' redeclared with different type (originally declared at arch/sparc/include/asm/oplib_32.h:67) - different modifiers
arch/sparc/prom/ranges.c:16:26: warning: symbol 'promlib_obio_ranges' was not declared. Should it be static?
arch/sparc/prom/ranges.c:17:5: warning: symbol 'num_obio_ranges' was not declared. Should it be static?
arch/sparc/prom/ranges.c:39:1: warning: symbol 'prom_adjust_ranges' was not declared. Should it be static?
arch/sparc/prom/ranges.c:69:13: warning: symbol 'prom_ranges_init' was not declared. Should it be static?
arch/sparc/prom/tree_32.c:286:22: warning: Using plain integer as NULL pointer
arch/sparc/prom/tree_32.c:286:38: warning: Using plain integer as NULL pointer

None of the warnings indicated any serious issues.

We are now sparse clean for 32 bit build in arch/sparc/prom.

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