staging: erofs: remove __EROFS_BIT

It's better to use pre-calculated values to make
on-disk definition more straight-forward and human-readable.

Since there is the only one user, let's remove
__EROFS_BIT entirely.

Suggested-by: Joe Perches <[e-mail]>
Signed-off-by: Gao Xiang <[e-mail]>
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

drivers/staging/erofs/erofs_fs.h

···
 /* 80 */__u8 reserved2[48];     /* 128 bytes */
 } __packed;
 
-#define __EROFS_BIT(_prefix, _cur, _pre)	enum {	\
-	_prefix ## _cur ## _BIT = _prefix ## _pre ## _BIT + \
-		_prefix ## _pre ## _BITS }
-
 /*
  * erofs inode data mapping:
  * 0 - inode plain without inline data A:
···
 	EROFS_INODE_LAYOUT_INLINE,
 	EROFS_INODE_LAYOUT_MAX
 };
+
+/* bit definitions of inode i_advise */
 #define EROFS_I_VERSION_BITS            1
 #define EROFS_I_DATA_MAPPING_BITS       3
 
 #define EROFS_I_VERSION_BIT             0
-__EROFS_BIT(EROFS_I_, DATA_MAPPING, VERSION);
+#define EROFS_I_DATA_MAPPING_BIT        1
 
 struct erofs_inode_v1 {
 /*  0 */__le16 i_advise;