drm/amd/display: Fix Silence Conversion Warnings in Dmub

drm/amd/display: Fix Silence Conversion Warnings in Dmub

Fix Conversion that might result in a loss of data  warnings in dmub/src/:

- dmub_dcn20/31/32/35/42/60/401.c: Add ASSERT(value <= 0xFF) and
  explicit (uint8_t) cast when storing REG_GET results into uint8_t
  debug struct fields. Add != 0 for bool assignments from uint32_t
  bitfield reads.
- dmub_reg.c: Cast va_arg shift value to uint8_t with ASSERT guard
  before passing to set_reg_field_value_masks().
- dmub_srv.c: Widen num_pending to uint64_t to match uint64_t
  arithmetic; use != 0 for bool assignments from unsigned expressions.

No functional change intended.

Reviewed-by: Dillon Varone <dillon.varone@amd.com>
Signed-off-by: Gaghik Khachatrian <gaghik.khachatrian@amd.com>
Signed-off-by: Chuanyu Tseng <chuanyu.tseng@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>