drm/amd/display: Ensure HPD source index is valid for dcn20/dcn201 link encoders

This patch adds a boundary check for the hpd_source index during the
link encoder creation process for dcn20/dcn201 IP's. The check ensures
that the index is within the valid range of the link_enc_hpd_regs array
to prevent out-of-bounds access.

Cc: Tom Chung <chiahsuan.chung@amd.com>
Cc: Rodrigo Siqueira <Rodrigo.Siqueira@amd.com>
Cc: Roman Li <roman.li@amd.com>
Cc: Alex Hung <alex.hung@amd.com>
Cc: Aurabindo Pillai <aurabindo.pillai@amd.com>
Cc: Harry Wentland <harry.wentland@amd.com>
Cc: Hamza Mahfooz <hamza.mahfooz@amd.com>
Signed-off-by: Srinivasan Shanmugam <srinivasan.shanmugam@amd.com>
Reviewed-by: Roman Li <roman.li@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>