drm/nouveau/pmu: Fix gp10b firmware guard

Most kernel configs enable multiple Tegra SoC generations, causing this
typo to go unnoticed. But in the case where a kernel config is strictly
for Tegra186, this is a problem.

Fixes: 989863d7 ("drm/nouveau/pmu: select implementation based on available firmware")
Signed-off-by: Aaron Kling <webgeek1234@gmail.com>
Signed-off-by: Danilo Krummrich <dakr@kernel.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20250218-nouveau-gm10b-guard-v2-1-a4de71500d48@gmail.com