epca.c: static functions and integer as NULL pointer fixes

drivers/char/epca.c:926:28: warning: Using plain integer as NULL pointer
drivers/char/epca.c:1841:2: warning: Using plain integer as NULL pointer

Forward declarations were already marked static, mark the definitions too.
drivers/char/epca.c:2493:6: warning: symbol 'digi_send_break' was not declared. Should it be static?
drivers/char/epca.c:2881:12: warning: symbol 'init_PCI' was not declared. Should it be static?

[akpm@linux-foundation.org: coding-style fixes]
Signed-off-by: Harvey Harrison <harvey.harrison@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>