ixgbe: Fix out-bounds warning in ixgbe_host_interface_command()

Replace union with a couple of pointers in order to fix the following
out-of-bounds warning:

  CC [M]  drivers/net/ethernet/intel/ixgbe/ixgbe_common.o
drivers/net/ethernet/intel/ixgbe/ixgbe_common.c: In function ‘ixgbe_host_interface_command’:
drivers/net/ethernet/intel/ixgbe/ixgbe_common.c:3729:13: warning: array subscript 1 is above array bounds of ‘u32[1]’ {aka ‘unsigned int[1]’} [-Warray-bounds]
 3729 |   bp->u32arr[bi] = IXGBE_READ_REG_ARRAY(hw, IXGBE_FLEX_MNG, bi);
      |   ~~~~~~~~~~^~~~
drivers/net/ethernet/intel/ixgbe/ixgbe_common.c:3682:7: note: while referencing ‘u32arr’
 3682 |   u32 u32arr[1];
      |       ^~~~~~

This helps with the ongoing efforts to globally enable -Warray-bounds.

Link: https://github.com/KSPP/linux/issues/109Co-developed-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
Tested-by: Dave Switzer <david.switzer@intel.com>
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>
Link: https://lore.kernel.org/r/20210527173424.362456-1-anthony.l.nguyen@intel.comSigned-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/net/ethernet/intel/ixgbe/ixgbe_common.c

@@ -3678,10 +3678,8 @@ s32 ixgbe_host_interface_command(struct ixgbe_hw *hw, void *buffer,
 				 bool return_data)
 {
 	u32 hdr_size = sizeof(struct ixgbe_hic_hdr);
-	union {
-		struct ixgbe_hic_hdr hdr;
-		u32 u32arr[1];
-	} *bp = buffer;
+	struct ixgbe_hic_hdr *hdr = buffer;
+	u32 *u32arr = buffer;
 	u16 buf_len, dword_len;
 	s32 status;
 	u32 bi;
@@ -3707,12 +3705,12 @@ s32 ixgbe_host_interface_command(struct ixgbe_hw *hw, void *buffer,
 
 	/* first pull in the header so we know the buffer length */
 	for (bi = 0; bi < dword_len; bi++) {
-		bp->u32arr[bi] = IXGBE_READ_REG_ARRAY(hw, IXGBE_FLEX_MNG, bi);
-		le32_to_cpus(&bp->u32arr[bi]);
+		u32arr[bi] = IXGBE_READ_REG_ARRAY(hw, IXGBE_FLEX_MNG, bi);
+		le32_to_cpus(&u32arr[bi]);
 	}
 
 	/* If there is any thing in data position pull it in */
-	buf_len = bp->hdr.buf_len;
+	buf_len = hdr->buf_len;
 	if (!buf_len)
 		goto rel_out;
 
@@ -3727,8 +3725,8 @@ s32 ixgbe_host_interface_command(struct ixgbe_hw *hw, void *buffer,
 
 	/* Pull in the rest of the buffer (bi is where we left off) */
 	for (; bi <= dword_len; bi++) {
-		bp->u32arr[bi] = IXGBE_READ_REG_ARRAY(hw, IXGBE_FLEX_MNG, bi);
-		le32_to_cpus(&bp->u32arr[bi]);
+		u32arr[bi] = IXGBE_READ_REG_ARRAY(hw, IXGBE_FLEX_MNG, bi);
+		le32_to_cpus(&u32arr[bi]);
 	}
 
 rel_out: