clk: at91: fix update bit maps on CFG_MOR write

The regmap update bits call was not selecting the proper mask, considering
the bits which was updating.
Update the mask from call to also include OSCBYPASS.
Removed MOSCEN which was not updated.

Fixes: 1bdf0232

 ("clk: at91: make use of syscon/regmap internally")
Signed-off-by: Eugen Hristev <eugen.hristev@microchip.com>
Link: https://lkml.kernel.org/r/1568042692-11784-1-git-send-email-eugen.hristev@microchip.com
Acked-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Reviewed-by: Claudiu Beznea <claudiu.beznea@microchip.com>
Signed-off-by: Stephen Boyd <sboyd@kernel.org>