qcacld-3.0: Fix mac address fallback when generation fails

Adapted from LineageOS/android_kernel_oneplus_sm8150@794b511

Recently, Chinese users have reported inline qcacld-3.0 failures
(although it's possible that this may pertain to a minority
of other users as well). This occurs as a result of wlan_mac.bin
failing to generate. Under normal circumstances, qcacld-3.0 would
fallback to a firmware provided mac address. However, OnePlus'
firmware byte-ordering results in a reversed address being fed to
the driver, breaking fallback logic and preventing WLAN from
getting off the ground entirely.

This reworks the original LineageOS patch to correct improper
in-loop variable declaration which triggers the following
compilation error not only on GCC, but current LLVM toolchains as
well:

../drivers/staging/qcacld-3.0/core/hdd/src/wlan_hdd_main.c:11006:7: error: GCC does not allow variable declarations in for loop initializers before C99 [-Werror,-Wgcc-compat]
        for (int i = 0; i < len / 2; i++) {
             ^

Co-authored-by: Peter Cai <peter@typeblog.net>
Signed-off-by: Adam W. Willis <return.of.octobot@gmail.com>

drivers/staging/qcacld-3.0/core/hdd/src/wlan_hdd_main.c

@@ -11002,6 +11002,17 @@ static int hdd_update_mac_addr_to_fw(struct hdd_context *hdd_ctx)
 	return 0;
 }
 
+static void reverse_byte_array(uint8_t *arr, int len)
+{
+	int i;
+
+	for (i = 0; i < len / 2; i++) {
+		char temp = arr[i];
+		arr[i] = arr[len - i - 1];
+		arr[len - i - 1] = temp;
+	}
+}
+
 /**
  * hdd_initialize_mac_address() - API to get wlan mac addresses
  * @hdd_ctx: HDD Context
@@ -11034,6 +11045,7 @@ static int hdd_initialize_mac_address(struct hdd_context *hdd_ctx)
 
 	/* Use fw provided MAC */
 	if (!qdf_is_macaddr_zero(&hdd_ctx->hw_macaddr)) {
+		reverse_byte_array(&hdd_ctx->hw_macaddr.bytes[0], 6);
 		hdd_update_macaddr(hdd_ctx, hdd_ctx->hw_macaddr, false);
 		update_mac_addr_to_fw = false;
 		return 0;