arch/x86: Wrap lines at 80 columns

Fix the following warning detected by checkpatch.pl:

WARNING: line over 80 characters

TEST=Build and run on Galileo Gen2

Change-Id: I3495cd30d1737d9ee728c8a9e72bd426d7a69c37
Signed-off-by: Lee Leahy <Leroy.P.Leahy@intel.com>
Reviewed-on: https://review.coreboot.org/18864
Tested-by: build bot (Jenkins)
Reviewed-by: Aaron Durbin <adurbin@chromium.org>

src/arch/x86/cbmem.c

@@ -21,7 +21,8 @@
 #if !defined(__PRE_RAM__)
 void __attribute__((weak)) backup_top_of_ram(uint64_t ramtop)
 {
-	/* Do nothing. Chipset may have implementation to save ramtop in NVRAM. */
+	/* Do nothing. Chipset may have implementation to save ramtop in NVRAM.
+	 */
 }
 
 static void *ramtop_pointer;