thermal/drivers/brcmstb_thermal: Use max to simplify brcmstb_get_temp

thermal/drivers/brcmstb_thermal: Use max to simplify brcmstb_get_temp

Use max() to simplify brcmstb_get_temp() and improve its readability.
Since avs_tmon_code_to_temp() returns an int, change the data type of
the local variable 't' from long to int.  No functional changes.

Signed-off-by: Thorsten Blum <thorsten.blum@linux.dev>
Signed-off-by: Daniel Lezcano <daniel.lezcano@kernel.org>
Reviewed-by: Florian Fainelli <florian.fainelli@broadcom.com>
Link: https://patch.msgid.link/20260402165616.895305-3-thorsten.blum@linux.dev