usb-misc: sisusbvga: Remove memory allocation logs

This patch remove three calls to dev_err() from sisusb_probe() as
reporting memory allocation failures is redundant:

 - Remove a call to dev_err() that was reporting unsuccesful call to
   kzalloc().

 - Remove two calls to dev_err() that were reporting unsuccesful calls
   to kmalloc().

One call to dev_err() reporting memory allocation is left unchanged as
the last patch of the series removes it.

Signed-off-by: Peter Senna Tschudin <peter.senna@collabora.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>