drm/amd/pm: Mundane typo fixes in the file amdgpu_pm.c

s/"an minimum"/"a minimum"/
s/"an maxmum"/"a maximum"/

Reviewed-by: Huang Rui <ray.huang@amd.com>
Acked-by: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Bhaskar Chowdhury <unixbhaskar@gmail.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>