Changed bd callbacks to use "bd_" prefix

This makes the block-device related operations more clearly block-device
related operations, and helps avoid possible conflicts with user
provided `lfs_bd_read/prog/erase` functions in the LFS_STATICCFG mode.

lfs.h

@@ -130,28 +130,28 @@ enum lfs_whence_flags {
 struct lfs_cfg {
     // Opaque user provided context that can be used to pass
     // information to the block device operations
-    void *ctx;
+    void *bd_ctx;
 
     // Read a region in a block. Negative error codes are propogated
     // to the user.
-    int (*read)(void *ctx, lfs_block_t block,
+    int (*bd_read)(void *ctx, lfs_block_t block,
             lfs_off_t off, void *buffer, lfs_size_t size);
 
     // Program a region in a block. The block must have previously
     // been erased. Negative error codes are propogated to the user.
     // May return LFS_ERR_CORRUPT if the block should be considered bad.
-    int (*prog)(void *ctx, lfs_block_t block,
+    int (*bd_prog)(void *ctx, lfs_block_t block,
             lfs_off_t off, const void *buffer, lfs_size_t size);
 
     // Erase a block. A block must be erased before being programmed.
     // The state of an erased block is undefined. Negative error codes
     // are propogated to the user.
     // May return LFS_ERR_CORRUPT if the block should be considered bad.
-    int (*erase)(void *ctx, lfs_block_t block);
+    int (*bd_erase)(void *ctx, lfs_block_t block);
 
     // Sync the state of the underlying block device. Negative error codes
     // are propogated to the user.
-    int (*sync)(void *ctx);
+    int (*bd_sync)(void *ctx);
 
     // Minimum size of a block read. All read operations will be a
     // multiple of this value.
@@ -226,12 +226,12 @@ struct lfs_cfg {
 // the lfs_cfg struct above.
 
 // Block device operations
-int lfs_read(lfs_block_t block,
+int lfs_bd_read(lfs_block_t block,
         lfs_off_t off, void *buffer, lfs_size_t size);
-int lfs_prog(lfs_block_t block,
+int lfs_bd_prog(lfs_block_t block,
         lfs_off_t off, const void *buffer, lfs_size_t size);
-int lfs_erase(lfs_block_t block);
-int lfs_sync(void);
+int lfs_bd_erase(lfs_block_t block);
+int lfs_bd_sync(void);
 
 // Required configuration
 #ifndef LFS_READ_SIZE