sparc32: fix sparse warnings in setup_32.c

Fix following warnings:
setup_32.c:106:15: warning: symbol 'cmdline_memory_size' was not declared. Should it be static?
setup_32.c:270:16: warning: symbol 'fake_swapper_regs' was not declared. Should it be static?
setup_32.c:368:55: warning: Using plain integer as NULL pointer

Add missing declaration of cmdline_memory_size and remove the local one in init_32.c
fake_swapper_regs was only used locally - so defined static.
When replacing 0 with NULL also add a few spaces around operators

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