The initialization via drmm_mutex_init can fail, so we need to check the
return code and escalate the failure.

The mutex initialization has been moved after all the other init steps
that can't fail, so we're always guaranteed to have those done and don't
have to check in the cleanup code.
Signed-off-by: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
Reviewed-by: Vinay Belgaumkar <vinay.belgaumkar@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240321195512.274210-1-daniele.ceraolospurio@intel.com