mtd: cfi_util: Fix unreachable code issue

Fix the following warning:

drivers/mtd/chips/cfi_util.c:112:3: warning: fallthrough annotation in unreachable code [-Wimplicit-fallthrough]
                   fallthrough;
                   ^
   include/linux/compiler_attributes.h:210:41: note: expanded from macro 'fallthrough'
   # define fallthrough                    __attribute__((__fallthrough__))
                                           ^
   drivers/mtd/chips/cfi_util.c:168:3: warning: fallthrough annotation in unreachable code [-Wimplicit-fallthrough]
                   fallthrough;
                   ^
   include/linux/compiler_attributes.h:210:41: note: expanded from macro 'fallthrough'
   # define fallthrough                    __attribute__((__fallthrough__))

by placing the fallthrough; statement inside ifdeffery.
Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>

drivers/mtd/chips/cfi_util.c

@@ -108,8 +108,8 @@ map_word cfi_build_cmd(u_long cmd, struct map_info *map, struct cfi_private *cfi
 #if BITS_PER_LONG >= 64
 	case 8:
 		onecmd |= (onecmd << (chip_mode * 32));
-#endif
 		fallthrough;
+#endif
 	case 4:
 		onecmd |= (onecmd << (chip_mode * 16));
 		fallthrough;
@@ -164,8 +164,8 @@ unsigned long cfi_merge_status(map_word val, struct map_info *map,
 #if BITS_PER_LONG >= 64
 	case 8:
 		res |= (onestat >> (chip_mode * 32));
-#endif
 		fallthrough;
+#endif
 	case 4:
 		res |= (onestat >> (chip_mode * 16));
 		fallthrough;