w1: use correct lock on error in w1_seq_show()

I noticed there was a problem here because Smatch complained:

	drivers/w1/slaves/w1_therm.c:416 w1_seq_show() warn:
	inconsistent returns 'mutex:&sl->master->mutex'.
	  Locked on:   line 416
	  Unlocked on: line 413

The problem is that we lock ->mutex but we unlock ->bus_mutex on error.
David Fries says that ->bus_mutex is correct and ->mutex is incorrect.

Fixes: d9411e57 ('w1: Add support for DS28EA00 sequence to w1-therm')
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Acked-by: Evgeniy Polyakov <zbr@ioremap.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>