drm/radeon: Prefer strscpy over strlcpy calls in radeon_atombios.c

Use the strscpy method instead of strlcpy method.

Fixes the below:

WARNING: Prefer strscpy over strlcpy

Cc: Christian König <christian.koenig@amd.com>
Cc: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Srinivasan Shanmugam <srinivasan.shanmugam@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>