Change calloc() so it passes Widnows build test

Code compiles under linux (not tested yet, I have no proxmark available right now)
Previous commit fails windows build test with:

src/cmdhfmfu.c: In function 'CmdHF14AMfuESave':
src/cmdhfmfu.c:4220:19: error: array subscript 'mfu_dump_t[0]' is partly outside array bounds of 'mfu_dump_t[0]' [-Werror=array-bounds]
 4220 |         end = dump->pages ;
      |                   ^~
In function 'GetMfuDumpFromEMul',
    inlined from 'CmdHF14AMfuESave' at src/cmdhfmfu.c:4202:15:
src/cmdhfmfu.c:4105:21: note: object of size 1076 allocated by 'calloc'
 4105 |     uint8_t *dump = calloc(MFU_MAX_BYTES + MFU_DUMP_PREFIX_LENGTH, sizeof(uint8_t));
      |                     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

client/src/cmdhfmfu.c

@@ -4102,20 +4102,20 @@ int CmdHF14MfuNDEFRead(const char *Cmd) {
 // utility function. Retrieves emulator memory
 static int GetMfuDumpFromEMul(mfu_dump_t **buf) {
 
-    uint8_t *dump = calloc(MFU_MAX_BYTES + MFU_DUMP_PREFIX_LENGTH, sizeof(uint8_t));
+    mfu_dump_t *dump = calloc(1, sizeof(mfu_dump_t));
     if (dump == NULL) {
         PrintAndLogEx(WARNING, "Fail, cannot allocate memory");
         return PM3_EMALLOC;
     }
 
     PrintAndLogEx(INFO, "downloading from emulator memory");
-    if (!GetFromDevice(BIG_BUF_EML, dump, sizeof(mfu_dump_t), 0, NULL, 0, NULL, 2500, false)) {
+    if (!GetFromDevice(BIG_BUF_EML, (uint8_t *)dump, MFU_MAX_BYTES + MFU_DUMP_PREFIX_LENGTH, 0, NULL, 0, NULL, 2500, false)) {
         PrintAndLogEx(WARNING, "Fail, transfer from device time-out");
         free(dump);
         return PM3_ETIMEOUT;
     }
 
-    *buf = (mfu_dump_t *)dump ;
+    *buf = dump ;
     return PM3_SUCCESS ;
 }