drm/amd/display: drop unnecessary NULL checks in debugfs

[ Upstream commit f8e12e77 ]

pipe_ctx pointer cannot be NULL when getting the address of
an element of the pipe_ctx array. Moreover, the MAX_PIPES is
defined as 6, so pipe_ctx is not NULL after the loop either.

Detected using the static analysis tool - Svace.

Signed-off-by: Alexey Kodanev <aleksei.kodanev@bell-sw.com>
Signed-off-by: Hamza Mahfooz <hamza.mahfooz@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Stable-dep-of: 892b41b1 ("drm/amd/display: Fix incorrect DSC instance for MST")
Signed-off-by: Sasha Levin <sashal@kernel.org>