clk: si5341: drop unused 'err' variable

clk: si5341: drop unused 'err' variable

'err' is assigned but never read:

  /drivers/clk/clk-si5341.c: In function ‘si5341_output_get_parent’:
  drivers/clk/clk-si5341.c:886:6: warning: variable ‘err’ set but not used [-Wunused-but-set-variable]

Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>
Link: https://lore.kernel.org/r/20200916161740.14173-5-krzk@kernel.org
Signed-off-by: Stephen Boyd <sboyd@kernel.org>