drm/xe: Prefer WARN() over BUG() to avoid crashing the kernel

Replace calls to XE_BUG_ON() with calls XE_WARN_ON() which in turn calls
WARN() instead of BUG(). BUG() crashes the kernel and should only be
used when it is absolutely unavoidable in case of catastrophic and
unrecoverable failures, which is not the case here.

Signed-off-by: Francois Dugast <francois.dugast@intel.com>
Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>