Changed lfs_crc to match more common API

In looking at the common CRC APIs out there, this seemed the most
common. At least more common than the current modified-in-place pointer
API. It also seems to have a slightly better code footprint. I'm blaming
pointer optimization issues.

One downside is that lfs_crc can't report errors, however it was already
assumed that lfs_crc can not error.

lfs_util.h

@@ -187,7 +187,7 @@ static inline uint32_t lfs_alignup(uint32_t a, uint32_t alignment) {
 }
 
 // Calculate CRC-32 with polynomial = 0x04c11db7
-void lfs_crc(uint32_t *crc, const void *buffer, size_t size);
+uint32_t lfs_crc(uint32_t crc, const void *buffer, size_t size);
 
 // Allocate memory, only used if buffers are not provided to littlefs
 static inline void *lfs_malloc(size_t size) {