ext/hal: stm32f3xx: Fix warnings for extraneous parentheses

Building with clang reports the following warnings:

stm32f3xx_hal_tim.c: error: equality comparison with extraneous
parentheses [-Werror,-Wparentheses-equality]
  else if((htim->State == HAL_TIM_STATE_READY))
           ~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~

Removing the extra () fixes the warning

Signed-off-by: Kumar Gala <kumar.gala@linaro.org>