char: misc: register chrdev region with all possible minors

register_chrdev will only register the first 256 minors of a major chrdev.
That means that dynamically allocated misc devices with minor above 255
will fail to open with -ENXIO.

This was found by kernel test robot when testing a different change that
makes all dynamically allocated minors be above 255. This has, however,
been separately tested by creating 256 serio_raw devices with the help of
userio driver.

Ever since allowing misc devices with minors above 128, this has been
possible.

Fix it by registering all minor numbers from 0 to MINORMASK + 1 for
MISC_MAJOR.

Reported-by: kernel test robot <oliver.sang@intel.com>
Cc: stable <stable@kernel.org>
Closes: https://lore.kernel.org/oe-lkp/202503171507.6c8093d0-lkp@intel.com


Fixes: ab760791 ("char: misc: Increase the maximum number of dynamic misc devices to 1048448")
Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@igalia.com>
Tested-by: Hou Wenlong <houwenlong.hwl@antgroup.com>
Link: https://lore.kernel.org/r/20250317-misc-chrdev-v1-1-6cd05da11aef@igalia.com


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