thermal: armada: Update Armada 380 thermal sensor coefficients

Improve the Armada 380 thermal sensor accuracy by using updated formula.
The updated formula is:
Temperature[C degrees] = 0.4761 * tsen_vsen_out - 279.1

Signed-off-by: Nadav Haklai <nadavh@marvell.com>
Signed-off-by: Gregory CLEMENT <gregory.clement@free-electrons.com>
Cc: <stable@vger.kernel.org> #v3.16
Signed-off-by: Eduardo Valentin <edubezval@gmail.com>