libfatx: Fix corruption when fatx_read size>bytes_per_cluster

[Ryzee119]

Im interacting with libfatx directly reading in a file ~4Mb then doing a CRC.

// Works okay
size_t offset = 0;
do {
  bytes_read = fatx_read(fs, "myfile.bin", offset , 16384, &buffer[offset]);`
  offset  += bytes_read
while (bytes_read > 0);

however

// CRC mismatch
size_t offset = 0;
do {
  bytes_read = fatx_read(fs, "myfile.bin", offset, 16384+1, &buffer[offset]);`
  offset  += bytes_read
while (bytes_read > 0);

We appear to be doing it right in fatx_write()

fatx/libfatx/fatx_file.c

Line 246 in 6777224

bytes_to_write = MIN(fs->bytes_per_cluster - cluster_offset, size - total_bytes_written);

This change fixes is.

The root causes it probably closer to doing reads that are not aligned on cluster boundaries.

Partition info below:

Device Path:         /C
  Partition Offset:    0x8ca80000 bytes
  Partition Size:      0x1f400000 bytes
  Volume Id:           5b206ddb
  Bytes per Sector:    512
  # of Sectors:        1024000
  Sectors per Cluster: 32
  # of Clusters:       31996
  Bytes per Cluster:   16384
  FAT Offset:          0x8ca81000 bytes
  FAT Size:            0x10000 bytes
  FAT Type:            16
  Root Cluster:        1
  Cluster Offset:      0x8ca91000 bytes