The clk_alpha_pll_stromer_plus_set_rate() function does not
sets the ALPHA_EN bit in the USER_CTL register, so setting
rates which requires using alpha mode works only if the bit
gets set already prior calling the function.

Extend the function to set the ALPHA_EN bit in order to allow
using fractional rates regardless whether the bit gets set
previously or not.

Fixes: 84da4892 ("clk: qcom: clk-alpha-pll: introduce stromer plus ops")
Signed-off-by: Gabor Juhos <j4g8y7@gmail.com>
Link: https://lore.kernel.org/r/20240508-stromer-plus-alpha-en-v1-1-6639ce01ca5b@gmail.comSigned-off-by: Bjorn Andersson <andersson@kernel.org>