ixgbevf: fix unused variable warning

The new ixgbevf_set_rx_buffer_len() function causes a harmless warnings
in configurations with large page size:

drivers/net/ethernet/intel/ixgbevf/ixgbevf_main.c: In function 'ixgbevf_set_rx_buffer_len':
drivers/net/ethernet/intel/ixgbevf/ixgbevf_main.c:1758:15: error: unused variable 'max_frame' [-Werror=unused-variable]

This rephrases the code so that the compiler can see the use of that
variable, making it slightly easier to read in the process.

Fixes: f15c5ba5 ("ixgbevf: add support for using order 1 pages to receive large frames")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Tested-by: Andrew Bowers <andrewx.bowers@intel.com>
Acked-by: Alexander Duyck <alexander.h.duyck@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>

drivers/net/ethernet/intel/ixgbevf/ixgbevf_main.c

@@ -1766,12 +1766,12 @@ static void ixgbevf_set_rx_buffer_len(struct ixgbevf_adapter *adapter,
 
 	set_ring_build_skb_enabled(rx_ring);
 
-#if (PAGE_SIZE < 8192)
-	if (max_frame <= IXGBEVF_MAX_FRAME_BUILD_SKB)
-		return;
+	if (PAGE_SIZE < 8192) {
+		if (max_frame <= IXGBEVF_MAX_FRAME_BUILD_SKB)
+			return;
 
-	set_ring_uses_large_buffer(rx_ring);
-#endif
+		set_ring_uses_large_buffer(rx_ring);
+	}
 }
 
 /**