builtin/config.c: rename check_blob_write() -> check_write()
builtin/config.c: rename check_blob_write() -> check_write()

The function will be reused to check for other conditions which prevent
write.

Signed-off-by: Kirill A. Shutemov <9b153e80bc985b32d577460a8a24e398d4182978@shutemov.name>
Signed-off-by: Junio C Hamano <a6723cc3f76163bf7adb636a73ac3b0ceb3e6b9b@pobox.com>

destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git