staging: exfat: Rename variable 'Attr' to 'attr'

Fix checkpatch warning: Avoid CamelCase
Change all occurrences of identifier "Attr" to "attr"

Signed-off-by: Pragat Pandya <pragat.pandya@gmail.com>
Link: https://lore.kernel.org/r/20200210183558.11836-16-pragat.pandya@gmail.com


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