kernfs/file.c: remove redundant error return counter assignment

Since previous 'rc = -EINVAL;', rc value doesn't change, so not
necessary to re-assign it again.

Signed-off-by: Lin Feng <linf@wangsu.com>
Link: https://lore.kernel.org/r/20220617091746.206515-1-linf@wangsu.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>