staging: rtl8192u: Replace symbolic permissions with octal permissions

Octal permissions should be used instead of symbolic ones for easier
reading.

WARNING: Symbolic permissions 'S_IRUGO | S_IWUSR' are not preferred.
Consider using octal permissions '0644'.
This warning is detected by checkpatch.pl

Signed-off-by: simran singhal <singhalsimran0@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>