char: misc: Use IS_ERR() for filp_open() return value

char: misc: Use IS_ERR() for filp_open() return value

filp_open() never returns NULL, it returns either a valid pointer or an
error pointer. Using IS_ERR_OR_NULL() is unnecessary. Additionally, if
filp were NULL, PTR_ERR(NULL) would return 0, leading to a misleading
error message.

Fixes: 74d8361be344 ("char: misc: add test cases")
Reported-by: kernel test robot <lkp@intel.com>
Reported-by: Dan Carpenter <dan.carpenter@linaro.org>
Closes: https://lore.kernel.org/r/202506132058.thWZHlrb-lkp@intel.com/
Signed-off-by: Alper Ak <alperyasinak1@gmail.com>
Acked-by: Thadeu Lima de Souza Cascardo <cascardo@igalia.com>
Link: https://patch.msgid.link/20251226230248.113073-1-alperyasinak1@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>