powerpc/pseries/vas: sysfs comments with the correct entries

VAS entry is created as a misc device and the sysfs comments
should list the proper entries

Reported-by: Matheus Castanho <mscastanho@ibm.com>
Signed-off-by: Haren Myneni <haren@linux.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/6dee950c7b72a4965c102208041f14a063cf5a8c.camel@linux.ibm.com