rt2800lib: fix some typos and punctuation in comments

fix some typos and punctuation in comments

Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@holoscopio.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>
[bart: ported the change from the older patch for rt2800usb & rt61pci]
Signed-off-by: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>