huawei: Fix implicit enum conversion

GCC 10 warns about this implicit conversion:

drivers/huaweimodem/radio-settings.c: In function ‘band_gsm_from_huawei’:
drivers/huaweimodem/radio-settings.c:107:10: error: implicit conversion from ‘enum ofono_radio_band_umts’ to ‘enum ofono_radio_band_gsm’ [-Werror=enum-conversion]
  107 |   return OFONO_RADIO_BAND_UMTS_ANY;

Member from the incorrect enum was returned, both had the value 0, so
the code would still work.

drivers/huaweimodem/radio-settings.c

@@ -104,7 +104,7 @@ static enum ofono_radio_band_gsm band_gsm_from_huawei(unsigned int band)
 	size_t i;
 
 	if (band == HUAWEI_BAND_ANY)
-		return OFONO_RADIO_BAND_UMTS_ANY;
+		return OFONO_RADIO_BAND_GSM_ANY;
 
 	for (i = ARRAY_SIZE(huawei_band_gsm_table) - 1; i > 0; i--) {
 		if (huawei_band_gsm_table[i].band_huawei & band)