drm/amd/display: fix pow() crashing when given base 0

commit d2e59d0 upstream.

[Why&How]
pow(a,x) is implemented as exp(x*log(a)). log(0) will crash.
So return 0^x = 0, unless x=0, convention seems to be 0^0 = 1.

Cc: stable@vger.kernel.org
Signed-off-by: Krunoslav Kovac <Krunoslav.Kovac@amd.com>
Reviewed-by: Anthony Koo <Anthony.Koo@amd.com>
Acked-by: Rodrigo Siqueira <Rodrigo.Siqueira@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/gpu/drm/amd/display/include/fixed31_32.h

@@ -431,6 +431,9 @@ struct fixed31_32 dc_fixpt_log(struct fixed31_32 arg);
  */
 static inline struct fixed31_32 dc_fixpt_pow(struct fixed31_32 arg1, struct fixed31_32 arg2)
 {
+	if (arg1.value == 0)
+		return arg2.value == 0 ? dc_fixpt_one : dc_fixpt_zero;
+
 	return dc_fixpt_exp(
 		dc_fixpt_mul(
 			dc_fixpt_log(arg1),