Documentation/devicetree/bindings/clock/ fix a typo

Corrected the word osciallator to oscillator in the file st,nomadik.txt.

Signed-off-by: Stefan Huber <steffhip@gmail.com>
Signed-off-by: Matthias Schid <aircrach115@gmail.com>
Signed-off-by: Simon Puels <simon.puels@gmail.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>