UBIFS: minor cleanup: use S_ISREG helper

Instead of using long "(inode->i_mode & S_IFMT) != S_IFREG" expression, use
shorted "!S_ISREG(inode->i_mode)".
Signed-off-by: NArtem Bityutskiy <Artem.Bityutskiy@nokia.com>

fs/ubifs/super.c

@@ -85,7 +85,7 @@ static int validate_inode(struct ubifs_info *c, const struct inode *inode)
 	if (ui->data_len < 0 || ui->data_len > UBIFS_MAX_INO_DATA)
 		return 4;
 
-	if (ui->xattr && (inode->i_mode & S_IFMT) != S_IFREG)
+	if (ui->xattr && !S_ISREG(inode->i_mode))
 		return 5;
 
 	if (!ubifs_compr_present(ui->compr_type)) {