imx: mx6ull: fix REFTOP_VBGADJ setting

imx: mx6ull: fix REFTOP_VBGADJ setting

The previous code wrote the contents of the fuse as is in the
REFTOP_VBGADJ[2:0], but this was wrong if you consider the contents of
the table in the code comment. This table is also different from the
table in the commit description. But then, which of the two is correct?
If it is assumed that an unprogrammed fuse has a value of 0 then for
backward compatibility of the code REFTOP_VBGADJ[2:0] must be set to
6 (b'110). Therefore, the table in the code comment can be considered
correct as well as this patch.

Fixes: 0b9fbf688420d ("imx: mx6ull: update the REFTOP_VBGADJ setting")
Signed-off-by: Dario Binacchi <dario.binacchi@amarulasolutions.com>