mfd: Fix twl-core oops while calling twl_i2c_* for unbound driver

Check inuse variable before trying to access twl_map to prevent
dereferencing of uninitialized variable.
Signed-off-by: NIlya Yanok <yanok@emcraft.com>
Cc: stable@kernel.org
Signed-off-by: NSamuel Ortiz <sameo@linux.intel.com>

drivers/mfd/twl-core.c

@@ -363,13 +363,13 @@ int twl_i2c_write(u8 mod_no, u8 *value, u8 reg, unsigned num_bytes)
 		pr_err("%s: invalid module number %d\n", DRIVER_NAME, mod_no);
 		return -EPERM;
 	}
-	sid = twl_map[mod_no].sid;
-	twl = &twl_modules[sid];
-
 	if (unlikely(!inuse)) {
-		pr_err("%s: client %d is not initialized\n", DRIVER_NAME, sid);
+		pr_err("%s: not initialized\n", DRIVER_NAME);
 		return -EPERM;
 	}
+	sid = twl_map[mod_no].sid;
+	twl = &twl_modules[sid];
+
 	mutex_lock(&twl->xfer_lock);
 	/*
 	 * [MSG1]: fill the register address data
@@ -420,13 +420,13 @@ int twl_i2c_read(u8 mod_no, u8 *value, u8 reg, unsigned num_bytes)
 		pr_err("%s: invalid module number %d\n", DRIVER_NAME, mod_no);
 		return -EPERM;
 	}
-	sid = twl_map[mod_no].sid;
-	twl = &twl_modules[sid];
-
 	if (unlikely(!inuse)) {
-		pr_err("%s: client %d is not initialized\n", DRIVER_NAME, sid);
+		pr_err("%s: not initialized\n", DRIVER_NAME);
 		return -EPERM;
 	}
+	sid = twl_map[mod_no].sid;
+	twl = &twl_modules[sid];
+
 	mutex_lock(&twl->xfer_lock);
 	/* [MSG1] fill the register address data */
 	msg = &twl->xfer_msg[0];