include unistd.h for getting ssize_t definitions
Fixes errors like

| In file included from src/sms.c:38:0:
| src/storage.h:32:1: error: unknown type name 'ssize_t'
| src/storage.h:36:1: error: unknown type name 'ssize_t'


Upstream-Status: Pending
Signed-off-by: Khem Raj <raj.khem@gmail.com>

Index: ofono-1.12/src/storage.h
===================================================================
--- ofono-1.12.org/src/storage.h	2013-01-04 10:01:24.137804178 -0800
+++ ofono-1.12/src/storage.h	2013-01-04 10:02:09.325806426 -0800
@@ -26,6 +26,7 @@
 #endif
 
 #include <fcntl.h>
+#include <unistd.h>
 
 int create_dirs(const char *filename, const mode_t mode);