restore spiffs data in boards.txt

[d-a-v]

(removed by mistake)

[earlephilhower]

This fixes my issue uploading SPIFFS.

Trying an upload with a 4M (no SPIFFS) setting, which should error, gives:

[SPIFFS] data   : /home/earle/Arduino/BearSSL_CertStore1/data
[SPIFFS] size   : -20
[SPIFFS] page   : 256
[SPIFFS] block  : 8192
terminate called after throwing an instance of 'std::bad_alloc'
  what():  std::bad_alloc

SPIFFS Create Failed!

With the removed if spiffs_kb>0, though, it would give a slightly more informative error
SPIFFS Not Defined for LOLIN(WEMOS) D1 R2 & mini, 80 MHz, Flash, 4M (no SPIFFS), v2 Lower Memory, Disabled, None, Only Sketch, 921600

Really a matter of preference, since it's an error and both are pretty obvious when you look at them.

[earlephilhower]

LGTM, fixed my issue/