debugfs: drop pointless nul-termination in debugfs_read_file_bool()

simple_read_from_buffer() doesn't care about any bytes in the buffer
beyond "available". Making the buffer nul-terminated is therefore
completely pointless.

Signed-off-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Link: https://lore.kernel.org/r/20210326151411.732220-1-linux@rasmusvillemoes.dk


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>