f2fs: fix some format WARNING in debug.c and sysfs.c

To fix:

WARNING: function definition argument 'struct f2fs_attr *' should also have an identifier name
+       ssize_t (*show)(struct f2fs_attr *, struct f2fs_sb_info *, char *);

WARNING: return sysfs_emit(...) formats should include a terminating newline
+       return sysfs_emit(buf, "(none)");

WARNING: Prefer 'unsigned int' to bare use of 'unsigned'
+               unsigned npages = NODE_MAPPING(sbi)->nrpages;

WARNING: Missing a blank line after declarations
+               unsigned npages = COMPRESS_MAPPING(sbi)->nrpages;
+               si->page_mem += (unsigned long long)npages << PAGE_SHIFT;

WARNING: quoted string split across lines
+               seq_printf(s, "CP merge (Queued: %4d, Issued: %4d, Total: %4d, "
+                               "Cur time: %4d(ms), Peak time: %4d(ms))\n",

Signed-off-by: Yangtao Li <frank.li@vivo.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>