drm/amd/display: Fix potential memory leak in DMUB hw_init

In the Linux kernel, the following vulnerability has been resolved:

drm/amd/display: Fix potential memory leak in DMUB hw_init

[Why]
On resume we perform DMUB hw_init which allocates memory:
dm_resume->dm_dmub_hw_init->dc_dmub_srv_create->kzalloc
That results in memory leak in suspend/resume scenarios.

[How]
Allocate memory for the DC wrapper to DMUB only if it was not
allocated before.
No need to reallocate it on suspend/resume.