thermal/drivers/k3_j72xx_bandgap: Simplify code in k3_bgp_read_temp()

The return value of vtm_get_best_value() always >= 0, remove always
false expression 'dtemp < 0' in if statement.

Signed-off-by: Rex Nie <rex.nie@jaguarmicro.com>
Link: https://lore.kernel.org/r/20241113005412.2254-1-rex.nie@jaguarmicro.com


Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>